Data transmission system, data transmission apparatus, data reception apparatus, and data transmission method

ABSTRACT

A data transmission system maintaining synchronization between transmission and reception even when a transmission apparatus, a reception apparatus and a transmission path do not operate on the same clock. Specifically, data packet is obtained by omitting a preamble and/or a parity from data generated by a data generation means and by adding a data length field and spare bits. The obtained data packet is set as an access unit and is transmitted from a transmission apparatus to a transmission path. A reception apparatus adds, to the received data, the preamble and/or the parity to reconstruct data, and adjusts a rate of a data reading clock for transmitting data from a reception-side buffer means to a data processing means a the basis of an accumulated amount in a clock control means.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a data transmission system in which atransmission path is shared by a plurality of communication apparatusesand which performs data transmission using synchronous channels, as wellas a data transmission method, a data transmission apparatus, and a datareception apparatus, and particularly relates to the system, method andapparatuses which achieve synchronization of operations between thetransmission apparatus and reception apparatus connected to each othervia the transmission path.

2. Background of the Related Art

In recent years, the study of the communication method for transmitting,via a common bus, digital data such as digitized video, audio data,computer data and the like is eagerly made. A conventional transmissionsystem, for example, the communication system disclosed in JapanesePublished Patent Application No. Hei. 9-107373, will be described as anexample, using FIG. 14. In FIG. 14, reference numeral 100 denotes atransmission path, and numeral 101 denotes a clock control means forcontrolling a clock of the transmission path 100. Further, referencenumeral 1410 denotes a transmission apparatus comprising a datageneration means 1411 and a first communication control means 112, andreference numeral 1420 denotes a reception apparatus comprising a dataprocessing means 1421 and a second communication control means 122.

Hereinafter, the operation will be described.

The transmission system shown in FIG. 14 transmits data from thetransmission apparatus 1410 to the reception apparatus 1420 via thetransmission path 100. The transmission path 100 operates on the basisof a clock which is controlled by the clock control means 101, and thefirst communication control means 112 in the transmission apparatus 1410and the second communication control means 122 in the receptionapparatus 1420, which are connected to the transmission path 100,extract the clock when receiving data from the transmission path 100,and utilizes the clock for data processing inside.

The transmission apparatus 1410 inputs the extracted clock to the datageneration means 1411. The data generation means 1411 generatestransmission data using the input clock and transmits the transmissiondata to the first communication control means 112. The firstcommunication control means 112 outputs the transmission data to thetransmission path 100.

In the reception apparatus 1420, the second communication control means122 receives the transmission data and transmits the same to the dataprocessing means 1421. Further, the second communication control means122 simultaneously extracts the clock and transmits the clock to thedata processing means 1421. The data processing means 1421 uses theextracted clock to process the transmission data.

In the procedure described above, the data generation in the datageneration means 1411 and the data processing in the data processingmeans 1421 are performed by using the same clock, and therebysynchronization between the transmission apparatus 1410 and thereception apparatus 1420 can be achieved and the transmission systemperforms operation without failure.

The network as described above is used for the vehicle-mountedmultimedia network MOST (Media Oriented Systems Transport) using opticalfiber for transmission, and the like, and the network and an apparatusconnected thereto operate by synchronizing clocks thereof, therebyreducing buffers and the like to be incorporated into the apparatus toattempt reduction in costs or facilitation of connection of variousapparatuses to the network.

Moreover, as for the network (IEEE1394) transmission of IEC60958 (i.e.,“IEC60958-1 First edition 1999-12”) format, for example, a demodulationapparatus and a signal processor which receive the IEC60958 format dataand demodulate the data in a transmission apparatus is disclosed inJapanese Published Patent Application No. 2000-149461.

As described above, in the conventional data transmission system, anddata transmission method, the transmission apparatus 1410, receptionapparatus 1420, and transmission path 100 operates on the same clock toperform data generation and processing, thereby maintainingsynchronization between transmission and reception.

However, in the conventional construction described above, when the datageneration means 1411 on the side of the transmission apparatus 1410 hasa specific clock and transmits the transmission data on the basis of thespecific clock, or in a system where while a clock source of the datageneration means 1411 and a clock source of the transmission path 100are the same, the transmission apparatus 1410 and the transmission path100 operate, respectively, on the clocks of different rates inspecifications, there is a problem that the synchronization in dataprocessing cannot be achieved.

Further, in a system where, while the data generation means 1411 and thetransmission path 100 operate on the clock of the same rate inspecifications, asynchronization is exactly caused due to clock sourcesthereof being different from each other, there is a problem that anoverflow or underflow of the transmission data occurs in thetransmission apparatus 1410 during the operation of the datatransmission system.

The present invention is made to solve the above-described problems, andan object of the present invention is to provide a data transmissionsystem, data transmission apparatus, data reception apparatus, and datatransmission method which can maintain synchronization betweentransmission and reception even when the transmission apparatus,reception apparatus, and transmission path do not operate on the sameclock.

BRIEF DESCRIPTION OF THE INVENTION

The data transmission system according to a first aspect of the presentinvention is a data transmission system in which one or moretransmission apparatus and one or more reception apparatus are connectedto each other via a transmission path and data are transmitted from thetransmission apparatus to the reception apparatus with using an accessunit which emerges at certain time intervals and is allocated for thetransmission path, wherein the transmission apparatus comprises a datapacket generation means for receiving transmission data which iscomposed of consecutive data frames and has a format which includes apreamble indicating a start of the data frame, or a parity for detectingan error in the data frame, or both of them, and omitting the preamble,or the parity, or both of them, from one or more data frames included inthe transmission data received within the certain time intervals, addingto this resultant a data length field indicating the number of bits ofsignificant data, and setting the remaining spare portion as spare bits,thereby generating a data packet composing the access unit over itsentire length, and the reception apparatus comprises a data extractionmeans for receiving the access unit, and adding the preamble, or theparity, or both of them, which have been omitted by the data packetgeneration means, thereby reconstructing the data frame.

Therefore, even when there is a difference between a clock rate of thetransmission path and a clock used for the processing inside thetransmission apparatus, the clock difference can be absorbed byadjusting the spare bit length, thereby realizing synchronization inoperations between the transmission apparatus and the receptionapparatus.

Further, according to the data transmission system of a second aspect ofthe present invention, in the data transmission system as defined in thefirst aspect, the reception apparatus comprises: a buffer means fortemporarily accumulating the data frames reconstructed by the dataextraction means, and a buffer control means for monitoring theaccumulated data amount in the buffer means and adjusting a data readingrate from the buffer means in accordance with the increase or decreasein the accumulated data amount.

Therefore, the reception apparatus can perform data processing at thesame clock rate as that of the transmission apparatus, thereby realizingthe synchronization of the system.

Further, according to the data transmission system of a third aspect ofthe present invention, in the data transmission system as defined in thefirst aspect, the transmission apparatus comprises a time-informationgeneration means for generating a time based on a clock of thetransmission data, and the data packet generation means also adds thetime-information as well as the data length field and sets the remainingspare portion as spare bits, thereby composing the access unit over theentire length, and the reception apparatus comprises: a buffer means fortemporarily accumulating the data frames reconstructed by the dataextraction means, a clock control means for reproducing the timegenerated by the transmission apparatus by using the time-informationwhich the data extraction means read from within the access unitconstructed by the data packet generation means, and a buffer controlmeans for adjusting a data reading rate from the buffer means based on aclock which is synchronized with a time reproduced by the clock controlmeans.

Therefore, even when there is a difference between a clock of thetransmission data and a clock of the transmission path, the receptionapparatus reads the time-information created from the clock on the sideof the transmission apparatus and adjusts the data reading rate, therebyrealizing synchronization of the system.

Further, according to the data transmission system of a fourth aspect ofthe present invention, in the data transmission system as defined in thefirst or second aspects of the invention, the data packet generationmeans also adds a preamble location pointer indicating a location of thefirst preamble in the data frame, and a type of the preamble of the dataframe, the preamble being indicated by the preamble location pointer, aswell as the data length field, and setting the remaining spare portionas spare bits, thereby constructing the access unit over the entirelength.

Therefore, even when the transmission data gets disconnected halfwayduring transmitting transmission data from the transmission apparatusvia the transmission path, reconstruction of a frame on the side of thereception apparatus can be easily realized with using informationindicating the location pointer and the type of the preamble, which isadded to the transmission data.

Further, according to the data transmission system of a fifth aspect ofthe present invention, in the data transmission system as defined in anyof the first to fourth aspects of the invention, the transmission dataformat includes a specific field having a value specific to anapplication, the data packet generation means also omits the specificfield as well as the preamble, or the parity, or both of them, and thedata extraction means also adds the specific field as well as thepreamble, or the parity, or both of them, thereby reconstructing thedata frame.

Therefore, by omitting unnecessary data for data transmission, datawhich can be transmitted for each packet via the transmission path canbe effectively utilized, and the reception apparatus adds the omitteddata to reconstruct the data frame, thereby demodulating thetransmission data properly.

Further, according to the data transmission system of a sixth aspect ofthe present invention, in the data transmission system as defined in anyof the first to fifth aspects of the invention, the data length fieldindicates the number of bits of spare bits.

Thereby, when packetizing the transmission data, it is possible tosecure a field into which an application can be arbitrarily written.

Further, the data transmission system according to a seventh aspect ofthe present invention is a data transmission system in which one or moretransmission apparatus and one or more reception apparatus are connectedto each other via a transmission path and data are transmitted from thetransmission apparatus to the reception apparatus with using an accessunit which emerges at certain time intervals and is allocated for thetransmission path, wherein the transmission apparatus comprises a datapacket generation means for receiving transmission data which iscomposed of consecutive data frames and has a data transfer rate, arelationship of an integer ratio being established between the datatransfer rate and a data transfer rate allocated for the transmissionpath, grouping into a processing unit a plurality of the data frames ofthe received transmission data and corresponding to a period equal to anintegral multiple of the time intervals at which the access unitemerges, dividing the processing unit into transmission path frames eachof which is the data amount which can be accommodated in the accessunit, thereby generating a data packet composing the access unitincluding the transmission path frame, and the reception apparatuscomprises a data extraction means for receiving the access unit,reconstructing the processing unit from one or more of the receivedaccess units, and further reconstructing the consecutive data frames.

Therefore, in a case where transmission data are transmitted withoutbeing omitted because of, for example, the preamble and the like beingunable to be omitted from the transmission data, even when there is adifference between a clock rate of the transmission path and a clockrate used for the processing inside the transmission apparatus, it ispossible to absorb the clock difference by grouping a plurality of dataframes into a processing unit, dividing the same into the transmissionpath frames respectively, and transmitting the same divided for eachaccess unit including the transmission path frame. Further, it ispossible to reconstruct the data frames from the access units on theside of the reception apparatus, thereby realizing the synchronizationof the system.

Further, according to the data transmission system of an eighth aspectof the present invention, in the data transmission system as defined inthe seventh aspect of the invention, the data packet generation meansenters one or more bits of synchronization data indicating a start ofthe processing unit into one or more access units, and the dataextraction means detects the starting location of the processing unit byreceiving the synchronization data.

Therefore, a data start location of the transmitted data can be easilydetected.

Further, according to the transmission system of a ninth aspect of thepresent invention, in the data transmission system as defined in theeighth aspect of the invention, the data packet generation means entersone or more bits of discrimination data which are different from a valueof the synchronization data, which discrimination data indicate that thesynchronization data are not included in the access unit, into positionin the access unit in which the synchronization data are not entered.

Therefore, error detection of the frame including synchronization datacan be eliminated, performing more reliable transmission.

Further, the data transmission system according to a tenth aspect of thepresent invention is a data transmission system in which one or moretransmission apparatus and one or more reception apparatus are connectedto each other via a transmission path and data are transmitted from thetransmission apparatus to the reception apparatus with using an accessunit which emerges at certain time intervals and is allocated for thetransmission path, wherein the transmission apparatus comprises a datapacket generation means for receiving transmission data which iscomposed of consecutive data frames, has a data transfer rate, arelationship of an integer ratio being established between the datatransfer rate and a data transfer rate allocated for the transmissionpath, and has a format including a preamble indicating a start of thedata frame, or a parity for detecting an error in the data frame, orboth of them, omitting the preambles, or the parities, or both of them,from a plurality of the data frames of the received transmission dataand corresponding to a period equal to an integral multiple of the timeintervals at which the access unit emerges to set the resultant as oneprocessing unit, dividing the processing unit into transmission pathframes each of which is the data amount which can be accommodated in theaccess unit, thereby generating a data packet composing the access unitincluding the transmission path frame, and the reception apparatuscomprises a data extraction means for receiving the access unit,reconstructing the processing unit from one or more of the receivedaccess units, and further adding the preambles, or the parities, or bothof them, which have been omitted by the data packet generation means,thereby reconstructing the data frames.

Therefore, even when there is a difference between a clock rate of thetransmission path and a clock rate used for the processing inside thetransmission apparatus, unnecessary data for transmitting transmissiondata are omitted and packetization into transmission data packet isperformed, and thereafter the transmission is made for each of theaccess units and thereby the clock difference can be absorbed. Furtherthe reception apparatus extracts the transmission data packet from anaccess unit of data received, and adds, to the transmission data packet,the data which have been omitted at the transmission, therebyreconstructing the data frame and realizing the synchronization betweenthe apparatuses in the system.

Further, according to the data transmission system of an eleventh aspectof the present invention, in the data transmission system as defined inthe tenth aspect of the invention, the data packet generation meansenters one or more bits of synchronization data indicating a start ofthe processing unit into one or more access units, and the dataextraction means detects the starting location of the processing unit byreceiving the synchronization data.

Therefore, a data start location of the transmitted data can be easilydetected.

Further, according to the data transmission system of a twelfth aspectof the present invention, in the data transmission system as defined inthe eleventh aspect of the invention, the data packet generation meansenters one or more bits of discrimination data which are different froma value of the synchronization data, which discrimination data indicatethat the synchronization data are not included in the access unit, intoposition in the access unit in which the synchronization data are notentered.

Therefore, error detection of the frame including synchronization datacan be eliminated, performing more reliable transmission.

Further, according to the data transmission system of a thirteenthaspect of the present invention, in the data transmission system asdefined in any of the tenth to twelfth aspects of the invention, thetransmission data format includes a specific field having a valuespecific to an application, and the data packet generation means alsoomits the specific field as well as the preamble, or the parity, or bothof them, and the data extraction means also adds the specific field aswell as the preamble, or the parity, or both of them, therebyreconstructing the data frame.

Therefore, by omitting unnecessary data for data transmission, datawhich can be transmitted for each packet via the transmission path canbe effectively utilized, and further the reception apparatus adds theomitted data to reconstruct data frames, thereby demodulatingtransmission data properly.

Further, according to the data transmission system of a fourteenthaspect of the present invention, in the data transmission system asdefined in any of the first to sixth and tenth to thirteenth aspects ofthe invention, the transmission data format is a format defined byIEC60958.

Therefore, the transmission data in format defined by IEC60958 can betransmitted from the transmission apparatus to the reception apparatusvia the transmission path with maintaining the synchronization.

Further, according to the data transmission system of a fifteenth aspectof the present invention, in the data transmission system as defined inany of the first to fourteenth aspects of the invention, thetransmission path is a serial bus.

Therefore, data can be more quickly transmitted via the transmissionpath.

Further, the data transmission apparatus according to a sixteenth aspectof the present invention is a data transmission apparatus connected to atransmission path, which transmits data with using an access unitallocated for the transmission path, and the data transmission apparatuscomprises a data packet generation means for receiving transmission datawhich is composed of consecutive data frames and has a format whichincludes a preamble indicating a start of the data frame, or a parityfor detecting an error in the data frame, or both of them, omitting thepreamble or the parity, or both of them, from one or more data framesincluded in the transmission data transmitted with using the accessunit, adding to this resultant a data length field indicating the numberof bits of significant data, and setting the remaining spare portion asspare bits, thereby generating a data packet composing the access unitover its entire length.

Therefore, a preamble or a parity, or both of them, which are notinvolved in the data processing, are omitted, and instead thereof, afield indicating the number of significant data bits required for datareproduction and spare bits for adjusting the transmission rate areadded to the data to be transmitted.

Further, according to the data transmission apparatus of a seventeenthaspect of the present invention, the data transmission apparatus asdefined in the sixteenth aspect of the invention comprises atime-information generation means for generating a time based on a clockof the transmission data, and in the data transmission apparatus thedata packet generation means also adds the time-information as well asthe data length field, and sets the remaining spare portion as sparebits, thereby generating a data packet composing an access unit over itsentire length.

Therefore, even when there is a difference between a clock of thetransmission data and a clock of the transmission path, time-informationcreated from the clock on the side of the transmission apparatus istransmitted, thereby realizing the synchronization of the system on thebasis of the time-information.

Further, according to the data transmission apparatus of an eighteenthaspect of the present invention, in the data transmission apparatus asdefined in the sixteenth aspect of the invention, the data packetgeneration means also adds a preamble location pointer indicating alocation of the first preamble in the data frame, and a type of thepreamble of the data frame, the preamble being indicated by the preamblelocation pointer, as well as the data length field, and sets theremaining spare portion as spare bits, thereby generating a data packetcomposing the access unit over its entire length.

Therefore, when the transmission data are transmitted via thetransmission path from the transmission apparatus, even if thetransmission data gets disconnected halfway, the reception apparatus caneasily realize reconstruction of a frame by using information indicatingthe location pointer and the type of the preamble, which is added to thetransmission data transmitted from the transmission apparatus.

Further, according to the data transmission apparatus of a nineteenthaspect of the present invention, in the data transmission apparatus asdefined in any of the sixteenth to eighteenth aspects of the invention,the transmission data format includes a specific field having a valuespecific to an application, and the data packet generation means alsoomits the specific field as well as the preamble, or the parity, or bothof them.

Therefore, by omitting unnecessary data for data transmission, datawhich can be transmitted for each packet via the transmission path canbe effectively utilized.

Further, according to the data transmission apparatus of a twentiethaspect of the present invention, in the data transmission apparatus asdefined in any of the sixteenth to nineteenth aspects of the invention,the data length field indicates the number of bits of spare bits.

Thereby, when packetizing the transmission data, it is possible tosecure a field into which an application can be arbitrarily written.

Further, the data transmission apparatus according to a twenty-firstaspect of the present invention is a data transmission apparatusconnected to a transmission path, which transmits data with using anaccess unit which emerges at certain time intervals and is allocated forthe transmission path, and the data transmission apparatus comprises adata packet generation means for receiving transmission data which iscomposed of consecutive data frames and has a data transfer rate, arelationship of an integer ratio being established between the datatransfer rate and a data transfer rate allocated for the transmissionpath, grouping into a processing unit a plurality of the data frames ofthe received transmission data and corresponding to a period equal to anintegral multiple of the time intervals at which the access unitemerges, dividing the processing unit into transmission path frames eachof which is the data amount which can be accommodated in the accessunit, thereby generating a data packet composing the access unitincluding the transmission path frame.

Therefore, even when the transmission data are transmitted without beingomitted because of, for example, the preamble and the like being unableto be omitted from the transmission data, the difference in clockbetween the transmission apparatus and the transmission path isabsorbed, thereby realizing synchronization.

Further, according to the data transmission apparatus of a twenty-secondaspect of the present invention, in the data transmission apparatus asdefined in the twenty-first aspect of the invention, the data packetgeneration means enters one or more bits of synchronization dataindicating a start of the processing unit into one or more access units.

Therefore, transmission data having a data start location which can beeasily detected can be obtained.

Further, according to the data transmission apparatus of a twenty-thirdaspect of the present invention, in the data transmission apparatus asdefined in the twenty-second aspect of the invention, the data packetgeneration means enters one or more bits of discrimination data whichare different from a value of the synchronization data, whichdiscrimination data indicate that the synchronization data are notincluded in the access unit, into position in the access unit in whichthe synchronization data are not entered.

Therefore, more reliable transmission data whose frame includingsynchronization data can be prevented from being erroneously detectedcan be obtained.

Further, the data transmission apparatus according to a twenty-fourthaspect of the present invention is a data transmission apparatusconnected to a transmission path, which transmits data with using anaccess unit which emerges at certain time intervals and is allocated forthe transmission path, and the data transmission apparatus comprises adata packet generation means for receiving transmission data which iscomposed of consecutive data frames, has a data transfer rate, arelationship of an integer ratio being established between the datatransfer rate and a data transfer rate allocated for the transmissionpath, and has a format including a preamble indicating a start of thedata frame, or a parity for detecting an error in the data frame, orboth of them, omitting the preambles, or the parities, or both of them,from a plurality of the data frames of the received transmission dataand corresponding to a period equal to an integral multiple of the timeintervals at which the access unit emerges to set the resultant as oneprocessing unit, dividing the processing unit into transmission pathframes each of which is the data amount which can be accommodated in theaccess unit, thereby generating a data packet composing the access unitincluding the transmission path frame.

Therefore, even when there is a difference between a clock rate of thetransmission path and a clock used for the processing inside thetransmission apparatus, unnecessary data for transmitting transmissiondata are omitted to be packetized, and then the transmission is made forevery number of bits of the access unit allocated for the transmissionpath, thereby absorbing the clock difference.

Further, according to the data transmission apparatus of a twenty-fifthaspect of the present invention, in the data transmission apparatus asdefined in the twenty-fourth aspect of the invention, the data packetgeneration means enters one or more bits of synchronization dataindicating a start of the processing unit into one or more access units.

Therefore, the transmission data having a data start location which canbe easily detected can be obtained.

Further, according to the data transmission apparatus of a twenty-sixthaspect of the present invention, in the data transmission apparatus asdefined in the twenty-fifth aspect of the invention, the data packetgeneration means enters one or more bits of discrimination data whichare different from a value of the synchronization data, whichdiscrimination data indicate that the synchronization data are notincluded in the access unit, into position in the access unit in whichthe synchronization data are not entered.

Therefore, more reliable transmission data whose frame includingsynchronization data can be prevented from being erroneously detectedcan be obtained.

Further, according to the data transmission apparatus of atwenty-seventh aspect of the present invention, in the data transmissionapparatus as defined in any of the twenty-fourth to twenty-sixth aspectsof the invention, the transmission data format includes a specific fieldhaving a value specific to an application, and the data packetgeneration means also omits the specific field as well as the preamble,or the parity, or both of them.

Therefore, by omitting unnecessary data for data transmission, datawhich can be transmitted for each packet via the transmission path canbe effectively utilized.

Further, according to the data transmission apparatus of a twenty-eighthaspect of the present invention, in the data transmission apparatus asdefined in any of the sixteenth to twentieth and twenty-fourth totwenty-seventh aspects of the invention, the transmission data format isa format defined by IEC60958.

Therefore, the transmission data in the format defined by IEC60958 canbe transmitted via the transmission path to the side of receptionapparatus with maintaining synchronization.

Further, according to the data transmission apparatus of a twenty-ninthaspect of the present invention, in the data transmission apparatus asdefined in any of the sixteenth to twenty-eighth aspects of theinvention, the transmission path is a serial bus.

Therefore, data can be more quickly transmitted via the transmissionpath.

Further, the data reception apparatus according to a thirtieth aspect ofthe present invention is a data reception apparatus which is connectedto a transmission path and receives a data packet obtained by omittingthe preamble, or the parity, or both of them, from one or more dataframes included in the transmission data which are transmitted withusing an access unit which emerges at certain time intervals and isallocated for the transmission path, adding to this resultant a datalength field indicating the number of bits of significant data, settingthe remaining spare portion as spare bits and composing the access unitover its entire length, and the data reception apparatus comprises adata extraction means for receiving the access unit and adding theretothe preamble of the transmission data, or the parity thereof, or both ofthem, which have been omitted, thereby reconstructing the data frame.

Therefore, data having a format in which a preamble or a parity, or bothof them, of the transmission data, which have been omitted at thetransmission are restored, can be reproduced.

Further, according to the data reception apparatus of a thirty firstaspect of the present invention, the data reception apparatus, asdefined in the thirtieth aspect of the invention, comprises: a buffermeans for temporarily accumulating the reconstructed data frames, and abuffer control means for monitoring the accumulated data amount in thebuffer means and adjusting a data reading rate from the buffer means inaccordance with the increase or decrease in the accumulated data amount.

Therefore, by adjusting data reading rate, the data processing can beperformed at the same clock rate as that of the transmission apparatus,thereby realizing synchronization of the system.

Further, according to the data reception apparatus of a thirty-secondaspect of the present invention, the data reception apparatus as definedin the thirtieth aspect of the invention, comprises: a buffer means fortemporarily accumulating the reconstructed data frames, a clock controlmeans for reproducing a time with using time-information which the dataextraction means read from within the constructed access unit, and abuffer control means for adjusting a data reading rate from the buffermeans based on a clock which is synchronized with a time reproduced bythe clock control means.

Therefore, even when there is a difference between a clock of thetransmission data and a clock of the transmission path, thetime-information created from the clock on the side of the transmissionapparatus is received and read, and the data reading rate is adjusted onthe basis of the time-information, thereby realizing synchronization ofthe system.

Further, the data reception apparatus according to a thirty-third aspectof the present invention is a data reception apparatus which isconnected to a transmission path and which receives a data packetobtained by omitting preambles each indicating a start of a data frame,or parities for detecting errors in the data frames, or both of them,from a plurality of data frames corresponding to a period equal to anintegral multiple of time intervals at which the access unit emerges,which data frames are transmitted with using the access unit whichemerges at certain time intervals and is allocated for the transmissionpath, to set the resultant as one processing unit, and dividing theprocessing unit into transmission path frames each of which is the dataamount which can be accommodated in the access unit, and composing theaccess unit including the transmission path frame, and the datareception apparatus comprises a data extraction means for receiving theaccess unit, reconstructing the processing unit from one or more of thereceived access units, adding to the processing unit the omittedpreamble or parity, or both of them, thereby reconstructing the dataframe.

Therefore, the received data are separated into transmission datapackets and the data which have been omitted at the transmission areadded to the transmission data packet, reproducing data having a formatin which a preamble or a parity, or both of them, of the transmissiondata, which have been omitted at the transmission, are restored.

Further, according to the data reception apparatus of thirty-fourthaspect of the present invention, in the data reception apparatus asdefined in the thirty-third aspect of the present invention, the dataextraction means detects the starting location of the processing unit byreceiving one or more access units including one or more bits ofsynchronization data indicating the start of the processing unit.

Therefore, a data start location of the transmitted data can be easilydetected.

Further, according to the data reception apparatus of a thirty-fifthaspect of the present invention, in the data reception apparatus asdefined in any of the thirtieth to thirty-fourth aspects of the presentinvention, the transmission data format includes a specific field havinga value specific to an application, and the data extraction means addsthe specific field as well as the preamble, or the parity, or both ofthem, according to a data frame of the transmission data, therebyreconstructing the data frame.

Therefore, the transmission data can be properly demodulated, therebyrealizing synchronization of the system.

Further, according to the data reception apparatus of a thirty-sixthaspect of the present invention, in the data reception apparatus asdefined in any of the thirtieth to thirty-fifth aspects of the presentinvention, the transmission data format is a format defined by IEC60958.

Therefore, transmission data in the format defined by IEC60958 can bereceived via the transmission path with maintaining synchronization withthe transmission apparatus.

Further, according to the data reception apparatus of a thirty-seventhaspect of the present invention, in the data reception apparatus asdefined in any of the thirtieth to thirty-sixth aspects of the presentinvention, the transmission path is a serial bus.

Therefore, the transmission data can be more quickly received via thetransmission path.

Further, the data transmission method according to a thirty-eighthaspect of the present invention comprises a data packet generation stepof omitting a preamble indicating a start of a data frame, or a parityfor detecting an error in the data frame, or both of them, from one ormore data frames included in the transmission data which is composed ofconsecutive data frames and has a format which includes the preamble, orthe parity, or both of them, adding to this resultant a data lengthfield indicating the number of bits of significant data of the frame,and setting the remaining spare portion as spare bits, and composing anaccess unit allocated for the transmission path over the entire length,thereby transmitting the access unit to the transmission path, and adata extraction step of receiving the access unit and adding to theaccess unit the preamble or the parity, or both of them, which have beenomitted in the data packet generation step, thereby reconstructing thedata frame.

Therefore, even when there is a difference between a clock rate of thetransmission path and a clock used for the processing inside thetransmission apparatus, the clock difference can be absorbed byadjusting the spare bit length, and further the reception apparatus addsthe data which have been omitted at the transmission, and can performthe data processing at the same clock rate as that of the transmissionapparatus by adjusting the data reading rate, thereby realizingsynchronization of the system.

Further, according to the data transmission method of a thirty-ninthaspect of the present invention, in the data transmission method asdefined in the thirty-eighth aspect of the present invention, thetransmission data format includes a specific field having a valuespecific to an application, and the data packet generation step omitsthe specific field as well as the preamble, or the parity, or both ofthem, and the data extraction step also adds the specific field as wellas the preamble, or the parity, or both of them, thereby reconstructinga frame.

Therefore, by omitting unnecessary data for data transmission, datawhich can be transmitted for each packet via the transmission path canbe effectively utilized. Further, the reception apparatus adds theomitted data to reconstruct data frame and thereby transmission data canbe demodulated properly, and therefore synchronization of the system canbe realized.

Further, the data transmission method according to a fortieth aspect ofthe present invention comprises: a data packet generation step ofreceiving transmission data which has a data transfer rate, arelationship of an integer ratio being established between the datatransfer rate and a data transfer rate allocated for a transmissionpath, and which transmission data is composed of consecutive dataframes, grouping into a processing unit a plurality of the data framesof the received transmission data and corresponding to a period equal toan integral multiple of time intervals at which the access unit emerges,dividing the processing unit into transmission path frames each of whichis the data amount which can be accommodated in the access unit, therebygenerating a data packet composing the access unit including thetransmission path frame, and a data extraction step of receiving theaccess unit, reconstructing the processing unit from one or more of thereceived access units, and further reconstructing the consecutive dataframes.

Therefore, in a case where transmission data are transmitted withoutbeing omitted because of, for example, the preamble and the like beingunable to be omitted from the transmission data, even when there is adifference between a clock rate of the transmission path and a clockrate used for the processing inside the transmission apparatus, it ispossible to absorb the clock difference by grouping a plurality of dataframes into a processing unit, dividing the same into the transmissionpath frames respectively, and transmitting the same divided for eachaccess unit including the transmission path frame. Further, it ispossible to reconstruct the data frame from the processing units on theside of the reception apparatus, thereby realizing synchronizationbetween the apparatuses in the system.

Further, the data transmission method according to a forty-first aspectof the present invention comprises: a data packet generation step ofreceiving transmission data which has a data transfer rate, arelationship of an integer ratio being established between the datatransfer rate and a data transfer rate allocated for a transmissionpath, and which transmission data is composed of consecutive data framesand has a format including a preamble indicating a start of the dataframe, or a parity for detecting an error in the data frame, or both ofthem, omitting the preamble, or the parity, or both of them, from aplurality of the data frames of the received transmission data andcorresponding to a period equal to an integral multiple of timeintervals at which the access unit emerges to set the resultant as oneprocessing unit, dividing the processing unit into transmission pathframes each of which is the data amount which can be accommodated in theaccess unit, thereby generating a data packet composing the access unitincluding the transmission path frame, and a data extraction step ofreceiving the access unit, reconstructing the processing unit from oneor more of the received access units, adding to the processing unit thepreamble, or the parity, or both of them, which have been omitted in thedata packet generation step, thereby reconstructing the data frame.

Therefore, even when there is a difference between a clock rate of thetransmission path and a clock used for the processing inside thetransmission apparatus, unnecessary data for transmitting thetransmission data are omitted and packetization is performed andthereafter transmission is made for every number of bits of the accessunit allocated for the transmission path, thereby absorbing the clockdifference. Further, the reception apparatus reconstructs the data framefrom the processing unit, thereby realizing synchronization betweenapparatuses in the system.

Further, according to the data transmission method of a forty-secondaspect of the present invention, in the data transmission method asdefined in the forty-first aspect of the present invention, thetransmission data format includes a specific field having a valuespecific to an application, and the data packet generation step omitsthe specific field as well as the preamble, or the parity, or both ofthem, and the data extraction step also adds the specific field as wellas the preamble, or the parity, or both of them, thereby reconstructinga frame.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram illustrating a configuration of a datatransmission system according to embodiments of the present invention.

FIG. 2 is a diagram illustrating an IEC60958 format.

FIG. 3 is a diagram illustrating an example of bi-phase modulation.

FIG. 4 is a diagram illustrating a preamble in IEC60958.

FIG. 5 is a diagram illustrating a transmission path format in MOST.

FIG. 6 is a diagram illustrating a process flow chart of a datatransmission apparatus according to the embodiments of the presentinvention.

FIG. 7 is a diagram illustrating a packetized format of transmissiondata used in the data transmission system according to a firstembodiment of the present invention.

FIG. 8 is a diagram illustrating a process flow chart of a datareception apparatus according to the embodiments of the presentinvention.

FIG. 9 is a diagram illustrating a clock control method according to theembodiments of the present invention.

FIG. 10 is a diagram illustrating a packet construction used in a datatransmission system according to a second embodiment of the presentinvention.

FIG. 11 is a diagram illustrating a packet construction used in a datatransmission system according to a third embodiment of the presentinvention.

FIG. 12 is a diagram illustrating a packet construction used in a datatransmission system according to a fourth embodiment of the presentinvention.

FIG. 13 is a block diagram illustrating a configuration of a datatransmission system according to a fifth embodiment of the presentinvention.

FIG. 14 is a block diagram illustrating a configuration of aconventional data transmission system.

FIG. 15 is a block diagram illustrating a configuration of a datatransmission system according to a sixth embodiment of the presentinvention.

FIG. 16 is a diagram illustrating a packet construction used in the datatransmission system according to the sixth embodiment of the presentinvention.

FIG. 17 is a diagram illustrating a method of transmitting transmissiondata frames in the data transmission system according to the sixthembodiment of the present invention.

FIG. 18 is a diagram illustrating a process flow chart of the datatransmission apparatus according to the sixth embodiment of the presentinvention.

FIG. 19 is a diagram illustrating a process flow chart of the datareception apparatus according to the sixth embodiment of the presentinvention.

FIG. 20 is a diagram illustrating a packet construction used in a datatransmission system according to a seventh embodiment of the presentinvention.

FIG. 21 is a diagram illustrating a method of transmitting transmissiondata frames in the data transmission system according to the seventhembodiment of the present invention.

FIG. 22 is a diagram illustrating a method of transmitting transmissiondata frames in a data transmission system according to an eighthembodiment of the present invention.

FIG. 23 is a diagram illustrating a process flow chart of the datatransmission apparatus according to the eighth embodiment of the presentinvention.

FIG. 24 is a diagram illustrating a process flow chart of the datareception apparatus according to the eighth embodiment of the presentinvention.

FIG. 25 is a diagram illustrating a method of transmitting transmissiondata frames in a data transmission system according to a ninthembodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION Embodiment 1

A configuration of a data transmission system in a first embodiment ofthe present invention is shown in FIG. 1. In FIG. 1, reference numeral100 denotes a transmission path, and numeral 101 denotes a clock controlmeans for controlling a clock of the transmission path 100. Further,reference numeral 110 denotes a transmission apparatus, and numeral 120denotes a reception apparatus. The transmission apparatus 110 comprisesa data generation means 111, a first communication control means 112, adata packet generation means 113, a transmission-side buffer means 114,and a transmission-side buffer control means 115. Further, the receptionapparatus 120 comprises a data processing means 121, a secondcommunication control means 122, a data extraction means 123, areception-side buffer means 124, and a reception-side buffer controlmeans 125, and a clock control means 126.

In this first embodiment, the transmission data are transmitted in aformat defined by IEC60958 (i.e. “IEC60958-1 First edition 1999-12”)from the data generation means 111. FIG. 2 is a diagram illustrating theIEC60958 format. As shown in FIG. 2, 1 frame is composed of 2 sub-framesin IEC60958 and further, 1 sub-frame is composed of 32 time slots. Then,slots 0 to 3 are for signals for synchronization discrimination, whichare called preambles, and slots 4 to 27 are slots allocated for datatransmission, on which 24 bits of data can be transmitted in 1sub-frame. Further, slot 28 is for a flag indicating reliability ofaudio data in the sub-frame (validity flag), slot 29 is for user datawhich can be freely set by a user, slot 30 is for a channel statusinformation, and slot 31 is a check bit (parity bit) of 28 bit datalength excluding the preamble part.

The bits of the slots 4 to 31 are subjected to bi-phase mark modulationfor dividing 1 slot into 2 symbols for representation, and transmitted.An example of the bi-phase modulation is shown in FIG. 3. As shown inFIG. 3, a state of the symbol is always inverted at the point where aslot changes. Further, in a case where data of the slot is “1”, thestate of the symbol is inverted at the center of the slot, and in a casewhere data of the slot is “0”, the state of the symbol is maintained. Byperforming this modulation, DC component of the transmission line can beminimized and clock reproduction can be easily performed.

Next, the preamble will be described with reference to the drawings.FIG. 4 is a diagram illustrating a preamble in IEC60958. There exist 3kinds of preambles, that is, preambles X and Y representing channel 1and channel 2 respectively and preamble Z representing a head of a blockcomposed of 192 frames. As shown in FIG. 4, a particular pattern whichis not represented in bi-phase modulated symbols is used for thepreamble.

A data format in the transmission path 100 in this first embodiment isshown in FIG. 5. In this first embodiment, a format in Media OrientedSystems Transport (hereinafter referred to as “MOST”) disclosed inPatrick Heck, Hervert Hetzel, Dave Knapp, Kevin Rolfes, Venkat Srinivas,Andreas Stiegler, Tony Susanto, and David Trager. Media OrientedSynchronous Transfer—A Network Protocol for High Quality, Low CostTransfer of Synchronous, Asynchronous, and Control Data on Fiber Optic.Presented at the 103rd AES Convention, 1997 Sep. 26-29, New York, isused in the transmission path 100. That is, in FIG. 5, reference numeral501 denotes a preamble in the transmission path format, numeral 502denotes a boundary descriptor, numeral 503 denotes a synchronous dataslot, numeral 504 denotes an asynchronous data slot, numeral 505 denotesa control frame, numeral 506 denotes a data for frame control andnumeral 507 denotes a parity. Then, the boundary descriptor 502indicates a location of a boundary between the synchronous data slot 503and the asynchronous data slot 504, and the data for frame control 506and the parity 507 are used for frame error detection and the like. InMOST, the transmission path formats are consecutively transmitted to therespective apparatuses connected to the transmission path 100. Then, therespective apparatuses perform data transmission using the synchronousdata slot 503, the asynchronous data slot 504 or the control frame 505,which are periodically transmitted from the transmission path 100.

In this first embodiment, the transmission data are to be transmittedusing the synchronous slot 503. Hereinafter, the transmission processwill be described with reference to the drawings.

FIG. 6 is a diagram illustrating a process flow chart of thetransmission apparatus in this first embodiment. When the flow starts(step 600), transmission data are input from the data generation means111 to the transmission-side buffer means 114 in the IEC60958 format.The transmission-side buffer control means 115 monitors the accumulateddata amount in the transmission-side buffer means 114, and, when acertain value, for example, 2 frames of data are accumulated, startsdata output from the transmission-side buffer means 114 to the datapacket generation means 113 (step 601).

A read start instruction is outputted to the data packet generationmeans 113 and the data packet generation means 113 transmits a readsignal to the transmission-side buffer means 114, thereby performing thestart of data output (step 602).

After receiving the first 1 frame of data, the data packet generationmeans 113 performs packetization of the transmission data (step 603).FIG. 7 is a diagram illustrating a packetized format of the transmissiondata. Here, FIG. 7( a) shows 1 frame of data before packetized and FIG.7( b) shows packetized data, in which reference numeral 701 denotes anindicator, numeral 702 denotes a data length, numeral 703 denotessignificant data in the packet, and numeral 704 denotes spare bits.Further, in figures, numerals described above the format indicate thenumber of bits allocated to the respective fields. In this firstembodiment, the frame shown in FIG. 7( a) is packetized by omitting bitsof preamble and parity as shown in FIG. 7( b) and transmitted to thetransmission path. These preamble and parity bits are required at thedata processing and are not used during the transmission between thetransmission apparatus 110 and the reception apparatus 120 via thetransmission path 100.

In FIG. 7( b), the indicator 701 is a flag indicating whether thesignificant data in the packet 703 subsequent thereto start from a headof a block or not, and “1” indicates a case where the data 703 startfrom the head of the block (preamble “Z”) and “0” indicates the othercases. Further, the data length 702 indicates the number of bits of thesignificant data included in the packet. The remaining part is spare bit704.

The data packet created in the process described above is synchronizedwith a clock of the transmission path supplied from the firstcommunication control means 112 (hereinafter referred to as“transmission path clock”) and is transmitted to the transmission pathwith the output timing of the synchronous channel of the transmissionpath (step 604).

Then, the data packet generation means 113 stores the accumulated dataamount in the transmission-side buffer means 114 at this time (step605). Then, with the timing of outputting the next synchronous data(step 606), data corresponding to the increased amount from theaccumulated data amount are packetized (step 607) and transmitted to thetransmission path (step 608).

Then, the number of bits of the spare bit 704 variably changes accordingto the number of bits of the significant data 703 to be packetized.

By repeating the operations as described above, the packets arecontinuously transmitted.

FIG. 8 is a diagram illustrating a process flow chart of the receptionapparatus in this first embodiment. When the flow starts (step 800), inthe reception apparatus 120, the second communication control means 122receives the data packet and transmits the data packet to the dataextraction means 123 in synchronization with the transmission path clock(step 801).

The data extraction means 123 reconstructs the transmission data fromthe packet (adds preamble and parity) (step 802), and transmits thereconstructed data to the reception-side buffer means 124 (step 803).For example, when receiving a packet in which the indicator represents“1”, the data extraction means adds a preamble of “Z” and starts theoutput, and thereafter “Y”, “X”, “Y”, . . . are sequentially added aspreambles.

The reception-side buffer means 124 temporarily accumulates thetransmission data, and starts to output the data to the data processingmeans 121 at the moment when a certain value, for example, 2 frames ofdata are accumulated. The controls for starting the output of thetransmission data, reading and the like are performed by thereception-side buffer control means 125.

In the reception apparatus 120 in this first embodiment, the clockcontrol means 126 performs processing for controlling an output clockrate to the data processing means 121 in accordance with the accumulateddata amount in the reception-side buffer means 124. The clock controlmeans 126 has a clock generating source inside. The clock generatingsource generates an output clock of a value approximate to atransmission data clock which is a clock of the transmission data outputfrom the data generation means 111, and further can slightly adjust therate of the generated output clock since the transmission data clock isreproduced by the reception apparatus 120.

Hereinafter, the control of the output clock by the clock control means126 will be described with reference to the drawings. FIG. 9 is adiagram illustrating the clock control method in this first embodiment.FIG. 9( a) shows the accumulated data amount in the reception-sidebuffer means 124 wherein the axis of ordinate represents the accumulateddata amounts and the axis of abscissa represents the elapsed time.Further, FIG. 9( b) shows the rates of the clock generated by the clockcontrol means 126 wherein the axis of ordinate represents clock ratesand the axis of abscissa represents the elapsed time.

The accumulated data amount in the reception-side buffer means 124starts to increase at time t3 (FIG. 9( a)). When the clock control means126 detects this increase, it increases the rate of the output clock tobe supplied to the buffer control means 125 (FIG. 9( b)). As a result ofincreasing the read rate, the increase in the accumulated data amountstops at time t6 and hence the clock control means 126 stops theprocessing for increasing the output clock rate.

Then, when the accumulated data amount starts to decrease at time t9,the clock control means 126 reduces the output clock rate. As describedabove, by controlling the output clock rate by the clock control means126, the transmission data are supplied from the reception-side buffermeans 124 to the data processing means 121 at almost the same rate asthe rate at which the data generation means 111 transmits thetransmission data.

Hereinafter, this first embodiment will be described in more detailswith using a specific example. Here, a system in which while the datageneration means 111 and the clock control means 101 operate on a clockof the same rate in specifications, asynchronization is exactly causeddue to the difference of the clock sources, will be considered, and asan example, a system in which 64 bits of data for 1 frame shown in FIG.7 are allocated to the synchronous data slot 503 in FIG. 5 inspecifications thus performing the transmission exactly, will beconsidered.

In a case where the clock sources are precisely identical to each other,the data packet generation means 113 performs packetization shown inFIG. 7( b), sets 54 bits as the number of bits allocated to the fieldfor the significant data in the packet 703 and 3 bits as the number ofbits allocated to the field for the spare bit 704 for a packet, andcontinues to transmit the packets to the transmission path 100, therebyperforming proper transmission.

However, in a case where a rate at which the data generation means 111transmits the transmission data is lower than a rate of the clockgenerated by the clock control means 101, when 3 bits are always set asthe number of bits of the field for the spare bit 704 in a like mannerand the transmission is performed, the data to be transmitted to thetransmission path 100 become short (underflow). In such a case, thetransmission apparatus of this first embodiment performs processing tosometimes transmit the packet in which the field for the spare bit 704is of 4 bits as well as the packet in which the field for the spare bit704 is of 3 bits, thereby absorbing the clock error.

Then, in the reception apparatus 120, the transmission data issequentially input to the reception-side buffer means 124 andtransmitted to the data processing means 121 on the basis of the readsignal of the reception-side buffer control means 125. In a case wherethe rate at which the data generation means 111 transmits thetransmission data is lower than the rate of the clock generated by theclock control means 101, the clock output from the clock control means126 becomes a slightly lower value than the transmission path clock onaverage, that is, becomes equal to the clock on which the datageneration means 111 transmits the transmission data.

On the other hand, in a case where a rate at which the data generationmeans 111 transmits the transmission data is higher than a rate of theclock generated by the clock control means 101, when 3 bits are alwaysset as the number of bits of the field for the spare bit 704 in a likemanner and the transmission is performed, the data, which cannot betransmitted to the transmission path 100, is gradually accumulated inthe transmission apparatus 110 (overflow). Also in such a case, thetransmission apparatus of this first embodiment performs processing tosometimes transmit the packet in which the number of bits of the fieldfor the spare bit 704 is 2 bits as well as the packet in which thenumber of bits of the field for the spare bit 704 is 3 bits, therebyabsorbing the clock error.

Then, in the reception apparatus 120, the transmission data issequentially input to the reception-side buffer means 124 andtransmitted to the data processing means 121 on the basis of the readsignal of the reception-side buffer control means 125. When the rate, atwhich the data generation means 111 transmits the transmission data, ishigher than the rate of the clock generated by the clock control means101, the clock output from the clock control means 126 becomes aslightly higher value than the transmission path clock on average, thatis, becomes equal to the clock on which the data generation means 111transmits the transmission data.

Thus, according to this first embodiment, a data packet obtained byomitting a preamble or a parity, or both of them, from the datagenerated by the data generation means 111 and adding the data length702 and the spare bit 704 is transmitted as an access unit from thetransmission apparatus 110 to the transmission path 100, and therebydata can be transmitted without shortage or excess by adjusting thelength of the spare bit 704 (the number of bits) even when there is adifference between the clock rate of the transmission path 100, which iscontrolled by the clock control means 101, and the clock rate which isused for the processing inside the transmission apparatus 110. Further,the reception apparatus 120 reconstructs data by adding, to the receiveddata, the preamble or parity, or both of them, which have been omitted,and the clock control means 126 adjusts the rate of data reading clockto the reception-side buffer 124 for transmitting data to the dataprocessing means 121, and thereby the data output from the datageneration means 111 on the side of the transmission apparatus 110 isprocessed at the same rate as the rate at which the data has beenoutput, by the data processing means 121 on the side of the receptionapparatus 120, even when there is a difference between the clock rate ofthe transmission path 100 and the clock rate of the transmissionapparatus 110 and reception apparatus 120.

Here, while in this first embodiment the indicator 701 represents “1”for the packet starting from a head of a block (a packet of preamble“Z”), the indicator 701 may represent “1” only when the transmissionstarts.

Embodiment 2

Next, a data transmission system and data transmission method accordingto a second embodiment of the present invention will be described. Thissecond embodiment is characterized in that a format in packetization isdifferent from that of the above-described first embodiment.Hereinafter, a description will be made with reference to the drawings.

FIG. 10 is a diagram illustrating a construction of a packet used in thedata transmission system in this second embodiment. In FIG. 10, a frameconstruction of transmission data shown in FIG. 10( a) is the same asthat shown in the first embodiment. Further, in FIG. 10( b), referencenumeral 1001 denotes an indicator, numeral 1002 denotes a data length,numeral 1003 denotes significant data in the packet, numeral 1004denotes spare bit, and numeral 1005 denotes arbitrary data.

In this second embodiment, not the number of bits of the significantdata in the packet 1003, but the number of bits of the spare bit 1004 isdescribed in the field for the data length 1002. For example, in asystem where while the data generation means 111 and the clock controlmeans 101 operate on a clock of the same rate in specifications,asynchronization is exactly caused due to the clock sources beingdifferent, a difference in the number of bits among the respectivetransmission frames is slight. That is, the variation in the number ofbits of the spare bit 1004 ranges between 1 bit and 2 bits and therefore2 bits are sufficient for the field for the data length 1002.

As a result, in this second embodiment, 6 bits of spare portion isgenerated for 1 frame, and arbitrary data can be written by anapplication in this spare area, that is, the area of the arbitrary data1005.

Then, a configuration as an apparatus in this second embodiment isidentical to that shown in FIG. 1 and the detailed description isomitted here.

The packet construction of this second embodiment described above iseffective particularly when synchronizing the clocks in a system wherethe clock of the data generation means 111 is different in rate from thetransmission path clock in specification, for example, in aconfiguration in which the data generation means 111 which generatesdata has a clock source of 48 kHz while the clock control means 101 hasa clock source of 44.1 kHz. That is, it is necessary that in such asystem, 48/44.1 times the data amount should be transmitted in a packetas compared to a case where the data generation means 111, whichgenerates data, has a clock source of 44.1 kHz. Therefore, in such acase, 4 bits among the portion of the arbitrary data 1005 shown in FIG.10 (6 bits) are used for data transmission and the variation in thenumber of bits of the significant data in the packet 1003 is absorbedinto the field for the spare bit 1004 and thereby the transmissionsystem can perform data transmission without failure.

Thus, according to this second embodiment, with noting that a variationin the number of bits of the spare bit 1004 is slight, the number ofbits of spare bit 1004 is described in the field for the data length1002, and the number of bits thereof is 2 bits, and further thevariation in the number of bits of the significant data in the packet1003 is absorbed using the field for the spare bit 1004 of 2 bits.Therefore, an area for the arbitrary data 1005 into which an applicationsoftware can write arbitrary data can be secured in the packet.

Embodiment 3

Next, a data transmission system and data transmission method accordingto a third embodiment of the present invention will be described. Thisthird embodiment is characterized in that a format in the packetizationis different from that of the above-described first embodiment.Hereinafter, description will be made with reference to the drawings.

FIG. 11 is a diagram illustrating a construction of a packet used in thedata transmission system in this third embodiment. In FIG. 11, a frameconstruction of transmission data shown in FIG. 11( a) is the same asthat shown in the first embodiment. Further, in FIG. 11( b), referencenumeral 1101 denotes a spare bit length, numeral 1102 denotes a preambletype, numeral 1103 denotes a preamble location pointer, numeral 1104denotes significant data in the packet, and numeral 1105 denotes sparebit.

This third embodiment is effective especially when the information forthe frame reconstruction is periodically notified to the receptionapparatus 120 so as to achieve the synchronization of the system in sucha system that while the data generation means 111 and the clock controlmeans 101 in FIG. 1 operate on the clock of the same rate inspecifications, asynchronization is exactly caused due to the differenceof the clock sources.

Here, while the frame information is periodically transmitted also bythe above-described first embodiment, the indicator 701 represents onlythat the significant data in the packet 703 subsequent thereto startfrom a head of a block or the other case (refer to FIG. 7( b)), in thefirst embodiment. Therefore, for example, in a case where a stream getsdiscontinued halfway, frames cannot be reconstructed until a packetincluding an indicator 701 indicating that significant data start from ahead of a block is received next. Then, in this third embodiment, apreamble type of the significant data in the packet or the like is addedto each packet to facilitate the frame reconstruction.

Then, a configuration as an apparatus of this third embodiment isidentical to that shown in FIG. 1, and the detailed description isomitted here.

The significant data 1104 and spare bit 1105 for 1 packet in this thirdembodiment are of 55 bits in total. The number of bits allocated to thefield for the spare bit 1105 is indicated by the spare bit length 1101of 2 bits.

Here, in a case where there is no asynchronization in clock between thedata generation means 111 and the clock control means 101, the timingfor 1 frame always coincides with that for 1 packet, and the significantdata 1104 is always of 54 bits and the spare bit 1105 is always of 1bit. On the other hand, in a case where there is asynchronization inclock between the data generation means 111 and the clock control means101, a value, which is indicated in the spare bit length 1101, is set to0 or 2, thereby performing adjustment. This adjustment is performed in amanner similar to that shown in the above-described second embodiment.

The preamble location pointer 1103 is of 5 bits, indicating where abreak of the sub-frame is located in the significant data in the packet1104. Since the significant data of a sub-frame is always of 27 bits(FIG. 11( a)), the break of the sub-frame is present anywhere within thefirst 27 bits in the significant data in the packet 1104. The preamblelocation pointer 1103 indicates the number of bits of up to the firstbreak of the sub-frame.

The preamble type 1102 is of 2 bits in which the preamble type of thesub-frame starting from the break indicated by the above-describedpreamble location pointer 1103 is described.

As shown in FIG. 2, 3 types of preambles, Z, X and Y, are present, andthe preambles are “Z” “Y” “X” “Y” . . . from the head of 1 block. Thatis, in cases where the preamble is Z and the preamble is X, the preambleof the subsequent sub-frame is Y while in a case where the preamble isY, there are 2 case, i.e., a case where the preamble of the subsequentsub-frame is Z and a case where it is X. Then, in the case where thepreamble is Y in the preamble type 1102, different symbols are allocatedbetween in the case where the preamble of the subsequent sub-frame is Zand in the case where it is X.

For example, in a case where the first preamble in the packet is Z, “00”is allocated, in a case where the first preamble in the packet is X,“01” is allocated, in a case where the first preamble is Y and thepreamble of the subsequent sub-frame is Z, “10” is allocated, and in acase where the first preamble is Y and the preamble of the subsequentsub-frame is X, “11” is allocated.

Then, the information in the preamble location pointer 1103 and thepreamble type 1102 are reflected in the frame reconstruction by thereception apparatus 120.

As described above, according to this third embodiment, since thepreamble location pointer 1103 is described in the field for thearbitrary data 1005 which is reserved in the second embodiment (FIG. 10(b)), when the reception apparatus reconstructs the frame, the receptionapparatus 120 can receive the information on the location and type ofthe preamble from the transmission apparatus 110. For example, even whenthe stream gets discontinued, the reception apparatus can easily realizethe frame reconstruction, thereby enhancing the reliability of thesystem.

Then, while in this third embodiment the spare bit length is provided asa field indicating the data length of the transmitted packet to indicatethe number of bits of the spare bit 1105, for example, the number ofbits of the significant data in the packet may be indicated as shown inthe above-described first embodiment instead of the number of bits ofspare bits, depending on the number of bits which can be transmitted foreach packet.

Embodiment 4

Next, a data transmission system and data transmission method accordingto a fourth embodiment of the present invention will be described. Thisfourth embodiment is characterized in that a format in the packetizationis different from that of the above-described first embodiment.Hereinafter, a description will be made with reference to the drawings.

FIG. 12 is a diagram illustrating a packet construction used in the datatransmission system in this fourth embodiment. In FIG. 12, the frameconstruction of the transmission data shown in FIG. 12( a) is the sameas that shown in the first embodiment. Further, in FIG. 12( b),reference numeral 1201 denotes a frame head indicator, numeral 1202denotes a preamble type, numeral 1203 denotes a spare bit indicator,numeral 1204 denotes significant data in the packet, and numeral 1205denotes spare bit.

The configuration of this fourth embodiment is effective especially whenthe information for frame reconstruction is periodically notified to thereception apparatus 120 so as to achieve synchronization of the systemin a system where the clock of the data generation means 111 isdifferent in rate from the transmission path clock in specifications,for example, in such a configuration that the data generation means 111which generates data has a clock source of 48 kHz while the clockcontrol means 101 has a clock source of 44.1 kHz.

Then, a configuration as an apparatus of this fourth embodiment isidentical to that shown in FIG. 1, and the detailed description isomitted here.

The significant data 1204 and the spare bit 1205 for one packet in thisfourth embodiment are of 60 bits in total. The length of the spare bit1205 is 0 bit or 6 bits, which is discriminated by the spare bitindicator 1203.

In this fourth embodiment, in the packet construction in thetransmission apparatus 110, in a case where the field for thesignificant data in the packet 1204 starts at a break of a sub-frame,the frame head indicator 1201 is set to “1”. Further, at this time, thetype of the sub-frame starting from the frame head is described usingthe preamble type (2 bits) 1202. On the other hand, in a case where thebreak of the sub-frame is located at a location other than the head ofthe packet, the frame head indicator 1201 is set to “0”.

The reception apparatus 120 reflects the frame head indicator 1201 andthe preamble type 1202 in the frame reconstruction.

As described above, according to this fourth embodiment, theconstruction is such that the spare bit 1205 is provided in the packetto absorb the variation in the number of bits and the frame headindicator 1201 indicating the head of the frame is provided in thepacket. Therefore, when the reception apparatus 120 reconstructs theframe, it can periodically receive the information on the location andtype of the preamble, and the reception apparatus 120 can easily realizeframe reconstruction, for example, even when the stream getsdiscontinued, thereby enhancing the reliability of the system.

Then, while in this fourth embodiment the spare bit indicator 1203 isprovided as a field indicating the data length of the transmitted packetto indicate the number of bits of the spare bit 1205, for example, thenumber of bits of the significant data in the packet may be indicated asshown in the above-described first embodiment instead of the number ofbits of spare bit, depending on the number of bits which can betransmitted for each packet.

Embodiment 5

Next, a data transmission system and data transmission method accordingto a fifth embodiment of the present invention will be described. Thisfifth embodiment is different from the above-described second embodimentin that the area of the arbitrary data 1005 shown in the secondembodiment (FIG. 10( b)) is used for time-information transmission forsynchronizing the transmission and reception. Hereinafter, a descriptionwill be made with reference to the drawings.

FIG. 13 is a diagram illustrating a configuration of the datatransmission system in this fifth embodiment, and in FIG. 13, the samereference numerals as those of FIG. 1 denote the same or correspondingparts, and reference numeral 1310 denotes a transmission apparatus,numeral 1313 denotes a data packet generation means, numeral 1314denotes a transmission-side buffer means, numeral 1315 denotes atransmission-side buffer control means, numeral 1316 denotes atransmission data clock extraction means, and numeral 1317 denotes atime-information generation means.

Further, reference numeral 1320 denotes a reception apparatus, numeral1323 denotes a data extraction means, numeral 1324 denotes areception-side buffer means, numeral 1325 denotes a reception-sidebuffer control means and numeral 1326 denotes a clock control means.

Hereinafter, the description will be made with emphasis on thecharacteristic operation of the present invention. In the transmissionapparatus 1310 of this fifth embodiment, the transmission data inputfrom the data generation means 111 is also input to the transmissiondata clock extraction means 1316, in which the extraction of thetransmission data clock, which is the clock of the transmission dataoutput from the data generation means 111, is performed. Thetransmission data clock extracted by the transmission data clockextraction means 1316 is transmitted to the time-information generationmeans 1317. This time-information generation means 1317 has a timer forgenerating time-information, and generates time-information by operatingthe timer with using the extracted transmission data clock.

The data packet generation means 1313 reads time-information from thetime-information generation means 1317 in synchronization with thetiming of transmitting a packet, and writes the time at the transmissiontiming in the field for the arbitrary data 1005 in FIG. 10.

On the other hand, in the reception apparatus 1320, the data extractionmeans 1323 receives the packet including the time-information, extractsthe time-information from the packet, and transmits the time-informationto the clock control means 1326.

The clock control means 1326 has a clock generating source inside. Theclock generating source generates an output clock of a value approximateto the transmission data clock, and can slightly adjust the rate of theoutput clock generated since the transmission data clock is reproducedin the reception apparatus 1320. The clock control means 1326sequentially compares the time-information created on the basis of thereceived transmission data clock and the time calculated from the outputclock from the clock generating source, and adjusts the rate of theoutput clock so that the time-information and the time coincide witheach other. This operation allows the clock of the transmission dataextracted by the transmission apparatus 1310 and the output clock whichis output by the clock control means 1326 in the reception apparatus1320 to be synchronized with each other achieving synchronization of thesystem.

In this way, according to this fifth embodiment, the time-informationgeneration means 1317 is provided in the transmission apparatus 1310,and the time-information at the data transmission timing is described inthe field for the arbitrary data 1005. The data extraction means 1323 inthe reception apparatus 1320 extracts the time-information, and theclock control means 1326 compares the extracted time-information and thetime-information based on the output clock generated from the clockgenerating source inside the clock control means 1326. Further, theclock control means 1326 adjusts the clock on the side of the receptionapparatus 1320 so that both of them coincide with each other, therebyachieving synchronization between the transmission apparatus 1310 andthe reception apparatus 1320 in the system.

Then, while in this fifth embodiment the transmission data clock isextracted from the transmission data, for example, the present inventionis applicable exactly in a like manner even in a system in which thetransmission clock is input separately from the transmission data.

Further, while in this fifth embodiment the time-information istransmitted for every packet, the transmission for every packet is notnecessarily required. For example, the time-information may betransmitted for every several packets and in packets in which notime-information is transmitted, the arbitrary data 1005 can be used foranother purpose, for example, for the same purpose as the spare bitswhich are shown in the first embodiment.

Further, while in this fifth embodiment the spare bit length 1002 isprovided as a field indicating the data length of the transmitted packetto indicate the number of bits of the spare bit 1004, the number of bitsof the significant data in the packet may be, for example, indicatedinstead of the number of bits of spare bits, depending on the number ofbits which can be transmitted for each packet as shown in the firstembodiment.

Embodiment 6

Next, a data transmission system and data transmission method accordingto this sixth embodiment will be described. While in each of theabove-described embodiments, cases where the clock source of the datageneration means 111 is different from the clock source of thetransmission path clock are described. Further, described in this sixthembodiment is be a case where while a clock of the transmission datagenerated by the data generation means 111 (hereinafter referred to as“transmission data clock”) is different in rate from the transmissionpath clock in specifications, clock sources thereof are the same.Hereinafter, a description will be made with reference to the drawings.

FIG. 15 is a diagram illustrating a configuration of the datatransmission system in this first embodiment. In FIG. 15, the samereference numerals as those in FIG. 1 denote the same or correspondingparts, and reference numeral 1501 denotes a clock control means, numeral1510 denotes a transmission apparatus, numeral 1511 denotes a datageneration means, and numeral 1512 denotes a first communication controlmeans. Further, reference numeral 1520 denotes a reception apparatus,numeral 1522 denotes a second communication control means, numeral 1524denotes a reception-side buffer means, numeral 1525 denotes areception-side buffer control means, and numeral 1527 denotes a secondclock control means.

Hereinafter, a description will be made with emphasis on thecharacteristic operation of the present invention. In the transmissionapparatus 1510 of this sixth embodiment, the first clock control means1501 generates the transmission path clock on the basis of thetransmission data clock, and transmits the transmission path clock tothe first communication control means 1512.

Then, the transmission path 100 operates in synchronization with thetransmission path clock, which is input to the first communicationcontrol means 1512.

On the other hand, in the reception apparatus 1520, the secondcommunication control means 1522 inputs the transmission path clockobtained from the transmission path 100 to the second clock controlmeans 1527. The second clock control means 1527 generates thetransmission data clock from the transmission path clock and suppliesthe transmission data clock to the reception-side buffer control means1525. The reception-side buffer control means 1525 controls the datareading from the reception-side buffer means 1524 using the transmissiondata clock. In this way, in this sixth embodiment, the clock of thetransmission apparatus 1510 is supplied from the data generation means1511 to generate the transmission path clock, and the receptionapparatus 1520 reproduces the transmission data clock on the side of thetransmission apparatus using the reverse process, thereby supplying thesame transmission data clock to the transmission apparatus 1510 and thereception apparatus 1520 and achieving synchronization between bothapparatuses, that is, synchronization of the system.

Hereinafter, the packetization of the transmission data frame in thissixth embodiment will be described using the drawings. FIG. 16 is adiagram illustrating a packet construction used in the data transmissionsystem of this sixth embodiment. In FIG. 16, a frame construction of thetransmission data shown in FIG. 16( a) is the same as that shown in thefirst embodiment. Further, in FIG. 16( b), reference numeral 1601denotes a preamble type, and numeral 1602 denotes significant data inthe packet. In this sixth embodiment, as in the above-described firstembodiment, 54 bits of significant data are made into 1 packet, and 2bits of preamble type are added thereto.

Next, a method of transmitting packetized transmission data frames inthis sixth embodiment will be described using FIG. 17. Then, in thissixth embodiment, the transmission data clock is based on 48 kHz and 64bits (that is, 1 frame) are transmitted in 1/48000 second. Further, thetransmission path clock is based on 44.1 kHz and a transmission pathframe for transmitting 64 bits in 1/44100 second is reserved.

The transmission system in this sixth embodiment generates atransmission path clock using a transmission data clock. Asynchronization relationship is established between the transmissiondata clock and the transmission path clock, and the synchronizationrelationship, while 160 transmission data frames (transmitting 64 bitsin 1/48000 second) are input, 147 transmission path frames aretransmitted, is established. Therefore, 160 transmission data frames aretransmitted using 147 transmission path frames, thereby establishingproper synchronization relationship.

To be specific, in this sixth embodiment, bits for a preamble and aparity are omitted from the frame shown in FIG. 16( a) and the preambletype 1601 is added as shown in FIG. 16( b), thereby forming atransmission data frame of 64 bits into a packet of 56 bits. Thus, thedata amount for 160 frames is 160×56=8960 bits. The number of framesrequired for transmitting these using transmission path frames is8960/64=140 frames, and the transmission can be made in a state where147−140=7 frames are spared.

The transmission data frames, each of which has been thus packetized as56 bits (FIG. 17( c)), are sequentially combined (FIG. 17( b)) and arethen transmitted 64 bits by 64 bits using the transmission path frame(FIG. 17( a)). In FIG. 17, the transmission data frames 1,2 . . . aretransmitted in the transmission path frames 8,9 . . . respectively inthis order, and the transmission of a total of 8960 bits of up totransmission path frame 147, that is, 160 transmission data frames iscompleted. By repeating these, the transmission data frames arecontinuously transmitted to the side of the reception apparatus 1520.

Then, in this sixth embodiment, data for packet synchronization betweenthe transmission apparatus 1510 and the reception apparatus 1520 areaccommodated in the transmission path frames 1 to 7 which have not beenused for the transmission of transmission data frames. For example, inthe transmission apparatus 1510, all the data of the transmission pathframe 1 is set to “1”, and the reception apparatus 1520 identifies asthe transmission path frame 1 the transmission path frame in which allthe data is set to “1” at the time of detecting the transmission pathframe, and recognizes that a data packet starts from the transmissionpath frame 8 which is the eighth frame counting from the transmissionpath frame 1.

At this time, if the allocation to the preamble type 1601 is other than“11”, for example, “00” is allocated for preamble Z, “01” for preamble Xand “10” for preamble Y, each of the transmission path frames includingpackets, that is, the transmission path frames 8 to 147 surely include abit of “0”, thereby preventing the transmission path frames includingpacket synchronization data from being erroneously identified. Then, thearbitrary data, for example, the music data in the case of transmittingaudio data, and the like, may be accommodated in the transmission pathframes 2 to 7, which are other than the transmission path frame 1 usedfor the transmission of the synchronization data, among the transmissionpath data frames 1 to 7 which do not include the transmission dataframes, and transmitted.

Hereinafter, the transmission process will be described with referenceto the drawings. FIG. 18 is a diagram illustrating a process flow chartof the transmission apparatus in this sixth embodiment. When the flowstarts (step 1800), the transmission data is input from the datageneration means 1511 to the transmission-side buffer means 114. Thetransmission-side buffer control means 115 monitors the accumulated dataamount in the transmission-side buffer means 114 and, when a certainvalue, for example, 2 frames of data are accumulated (step 1801), startsa process of data output to the data packet generation means 1513 (step1802). That is, the data packet generation means 1513 initiallytransmits the transmission path frames 1 to 7 in synchronization withthe timing of the transmission path clock (step 1803). Then, the datapacket generation means 1513 reads 1 frame of data from thetransmission-side buffer means 114 and performs the packetization shownin FIG. 16 (step 1804). Then, when the data packet generation means 1513does not hold data for 1 transmission path frame, that is, 64 bits ofdata in this sixth embodiment, which are to be transmitted subsequently(step 1805), the process is returned to step 1804, and 1 frame oftransmission data are read from the transmission-side buffer means 114and packetized.

Then, when the timing of outputting data to the transmission path framecomes (step 1806), data of 1 transmission path frame, that is, 64 bitsof data in this six embodiment, are output to the transmission path(step 1807). Then, processes of step 1805 to step 1807 are repeateduntil the data packet generation means 1513 outputs the transmissionpath frame 147 in FIG. 17, and the output of the transmission path frame147 is completed (step 1808), and then the processes of step 1803 tostep 1809 are repeated. Thereby, the packets are continuouslytransmitted.

FIG. 19 is a diagram illustrating a process flow chart of the receptionapparatus in this sixth embodiment. When the flow starts (step 1900),the reception apparatus 1520 receives the transmission path frames (step1901) and, when the data of the transmission path frame indicates aframe including synchronization data indicating transmission path frame1 (step 1902), starts the process (step 1903). Subsequently, the dataextraction means 1523 receives transmission path frame 2 to transmissionpath frame 7 subsequent to the transmission path frame 1 (step 1904),and the data extraction means 1523 subsequently receives thetransmission path frames (step 1905). Then, the data extraction means1523 processes data for transmission data frame from the receivedtransmission path frames, reconstructs the sub-frames, and outputs thesub-frames to the reception-side buffer means 1524 (step 1906). Then,processes of step 1905 to step 1906 are repeated until the transmissionpath frame 147 in FIG. 17 is received, and the process of transmissionpath frame 147 is completed (step 1907), and then processes of step 1901to step 1908 are repeated.

Data accumulated in the reception-side buffer 1524 are read with thesame clock as the transmission data clock in the transmission apparatus1510 and transmitted to the data processing means 121.

In this way, according to this sixth embodiment, in a case where whilethe clock source of the data generation means 1511 and the clock sourceof the transmission path 100 are the same, the clock rate of thetransmission data output from the data generation means 1511 isdifferent from the clock rate of the transmission path 100. That is, ina system operating based on the transmission data clock of 48 kHz andthe transmission path clock of 44.1 kHz, the transmission apparatus 1510creates the transmission path clock from the transmission data clock inthe first clock control means 1501, packetizes frames of thetransmission data as 56 bits, and sequentially combines the packetizedframes, and thereafter transmits the frames 64 bits by 64 bits withusing the transmission path frame, and the reception apparatus 1520receives the transmission path frame and the transmission path clock andcreates the transmission data clock from the transmission path clock inthe second clock control means 1527, and outputs the transmission datato the data processing means 121 on the basis of the transmission dataclock, and therefore the synchronized transmission between thetransmission apparatus 1510 and the reception apparatus 1520 can berealized.

Then, while in this sixth embodiment the transmission data clock isoutput from the data generation means 1511 to the transmission apparatus1510 and the first clock control means 1501 generates the transmissionpath clock from the transmission data clock, any configuration may beadopted as long as the configuration is one in which the transmissiondata clock and the transmission path clock are generated from the sameclock source. For example, the configuration may be one in which thefirst clock control means 1501 exists in another apparatus on thetransmission path 100, and in this case, the data generation means 1511receives the transmission path clock generated by the first clockcontrol means 1501 in the other apparatus, and creates the transmissiondata clock from the received transmission path clock.

Further, while in this sixth embodiment each of 64 bits of thetransmission path frame 1 accommodates “1”, it is not necessarilyrestricted to this value. For example, a frame other than thetransmission path frame 1 may be for synchronization data, or aplurality of frames may be used for synchronization data. Further, onlyone or more bits of the frame may be used as a mark for the transmissionpath frame including synchronization data, and the other bits may beused for another purpose, for example, for arbitrary data. Further,while in this sixth embodiment a system where the transmission dataframe is transmitted on the basis of 48 kHz and the transmission pathframe is transmitted on the basis of 44.1 kH is shown, they are notrestricted to these numeric values, and any system is applicable bychanging the number of transmission data frames and the number of thetransmission path frames as long as the system is one in which the clocksources of the transmission data frame and the transmission path frameare common. For example, in a system where the transmission data frameis transmitted on the basis of 44.1 kHz and the transmission path frameis transmitted on the basis of 48 kHz the synchronization relationshipthat while 147 transmission data frames are input, 160 transmission pathframes are transmitted, is established, and therefore in a case wherepacketization is performed on the basis of the method in this sixthembodiment and 56 bits of data are transmitted in 1 transmission pathframe, when the transmission path for transmitting 56 bits in 1/48000second is reserved, data can be transmitted using 147 transmission pathframes and the remaining 13 transmission path frames can be used for thetransmission of synchronization data and the transmission of arbitrarydata.

Embodiment 7

Next, a data transmission system and data transmission method accordingto this seventh embodiment will be described. This seventh embodiment ischaracterized in that a format in packetization and a method oftransmission to the transmission path are different from those for theabove-described sixth embodiment. Hereinafter, a description will bemade with reference to the drawings. Then, an apparatus configuration inthis seventh embodiment is similar to that shown in FIG. 15, and thedetailed description will be omitted here.

FIG. 20 is a diagram illustrating a packetization of the transmissiondata frame in this seventh embodiment. In FIG. 20, the transmission dataframe construction shown in FIG. 20( a) is the same as that shown in thefirst embodiment. Further, in FIG. 20( b), reference numeral 2001denotes significant data in the packet. In this seventh embodiment, onlythe significant data of the transmission data frame are extracted andpacketized.

A method of transmitting the packetized transmission data frames in thisseventh embodiment is shown in FIG. 21. Then, the relationship betweenthe transmission data frame clock and the transmission path frame clockin this seventh embodiment is the same as that in the case of theabove-described sixth embodiment, and the relationship between thetransmission data frame and the transmission path frame is similar tothe relationship in the above-described sixth embodiment. That is, 160transmission data frames are transmitted using 147 transmission pathframes, thereby establishing proper synchronization relationship.

In this seventh embodiment, as shown in FIG. 20( b), a transmission dataframe of 64 bits is formed into a packet of 54 bits. Thereby, the dataamount for 160 frames are 160×54=8640 bits. The number of framesrequired for transmitting these using the transmission path frame is8640/64=135 frames, and in this seventh embodiment, the transmission canbe made in a state where 147−135=12 frames are spared.

The transmission data frames each of which has been thus packetized as54 bits (FIG. 21( c)) are sequentially combined (FIG. 21( b)) andthereafter are transmitted 64 bits by 64 bits using the transmissionpath frames (FIG. 21( a)). In FIG. 21, the transmission data frames 1,2. . . are transmitted in the transmission path frames 13,14 . . .respectively in this order, and the transmission of a total of 8640 bitsof up to transmission path frame 147, that is, 160 transmission dataframes is completed. By repeating these, the transmission data framesare continuously transmitted to the side of the reception apparatus1520.

Then, in this seventh embodiment, any of the transmission path frames 1to 12 which have not been used for the transmission of the transmissiondata frames, or some frames thereof are used to synchronize thetransmission apparatus 1510 and the reception apparatus 1520 inreceiving packets. For example, the synchronization data 2002 in whicheach of 64 bits is set to “0” is accommodated in the transmission pathframe 12 and when the reception apparatus 1520 detects the transmissionpath frame 12 including the synchronization data 2002 in which each of64 bits is set to “0”, the reception apparatus 1520 recognizes that adata packet starts from the subsequent frame.

Further, as another example, data to be accommodated in each of 64 bitsof the transmission path frame 11 is 1 and data to be accommodated ineach of 64 bits of the transmission path frame 12 is 0, and thereception apparatus 1520 recognizes that a data packet starts from aframe detected subsequent to the transmission path frame 11 in whicheach of 64 bits is set to “1” and the transmission path frame 12 inwhich each of 64 bits is set to “0”.

In this way, according to this seventh embodiment, in a case where whilethe clock source of the data generation means 1511 and the clock sourceof the transmission path 100 are the same, the clock rate of thetransmission data output from the data generation means 1511 isdifferent from the clock rate of the transmission path 100, that is, ina system where the transmission data frame is transmitted on the basisof 48 kHz and the transmission path frame is transmitted on the basis of44.1 kHz, the transmission apparatus 1510 creates the transmission pathclock from the transmission data clock in the first clock control means1501, packetizes the frame of the transmission data as 54 bits, andsequentially combines the packetized frames, and thereafter transmitsthe frames 64 bits by 64 bits using transmission path frame, and thereception apparatus 1520 receives the transmission path frame and thetransmission path clock and creates the transmission data clock from thetransmission path clock in the second clock control means 1527, andoutputs the transmission data to the data processing means 121 on thebasis of the transmission data clock, and therefore the synchronizedtransmission between the transmission apparatus 1510 and the receptionapparatus 1520 can be realized.

Then, while in this seventh embodiment the transmission data clock isoutput from the data generation means to the transmission apparatus andthe first clock control means generates the transmission path clock fromthe transmission data clock, any configuration may be adopted as long asthe configuration is one in which the transmission data clock and thetransmission path clock are generated from the same clock source as inthe above-described sixth embodiment.

Further, a method of packet reception synchronization in this seventhembodiment is an example, and the method is not necessarily restrictedthereto. For example, frames other than frames used for synchronizationamong the transmission path frames 1 to 12 may be used for thetransmission of arbitrary data and the like.

Further, while in this seventh embodiment a system operating based onthe transmission data frame of 48 kHz and based on the transmission pathframe of 44.1 kHz is shown, they are not restricted to these numericvalues, and any system is applicable by changing the number oftransmission data frames and the number of transmission path frames aslong as the system is one in which the clock sources of the transmissiondata frame and the transmission path frame are common.

Embodiment 8

Next, a data transmission system and data transmission method accordingto this eighth embodiment will be described. While in each of theabove-described embodiments, the system and method in which thetransmission apparatus omits data which need not be transmitted usingthe transmission path, among the transmission data, to generate datapacket performing transmission are described, described in this eighthembodiment will be a case where when while the clock of the transmissiondata is different in rate from the clock of the transmission path inspecifications, the clock sources are the same, all the bits of thetransmission data are transmitted without omitting unnecessary data.Hereinafter, a description will be made with reference to the drawings.Then, an apparatus configuration in this eighth embodiment is similar tothat shown in FIG. 15, and a detailed description is omitted here.

FIG. 22 is a diagram illustrating a method of transmitting transmissiondata frames in this eighth embodiment. Then, in this eighth embodiment,the transmission data clock is based on 48 kHz and 64 bits (that is, 1frame) are transmitted in 1/48000 second. Further, the transmission pathclock is based on 44.1 kHz and a transmission path frame fortransmitting 72 bits in 1/44100 second is reserved.

In a transmission system of this eighth embodiment, omission of dataincluded in the transmission data is not performed unlike in the casesof the respective embodiments described above. Further, a transmissionpath clock is generated using a transmission data clock. Then, in thiseighth embodiment, the transmission data clock is based on 48 kHz andthe transmission path clock is based on 44.1 kHz, and the transmissionpath clock is faster than the transmission path clock, and therefore itis necessary that the transmission path frame should be made larger thanthe transmission data frame. Further, in the transmission system of thiseighth embodiment, the synchronization relationship similar to thoseshown in the above-described sixth and seventh embodiments isestablished and 160 transmission data frames are transmitted using 147transmission path frames, thereby establishing proper synchronizationrelationship.

To be specific, in this eighth embodiment, the transmission data frameof 64 bits obtained by omitting nothing, which is shown in FIG. 22( c),is transmitted. Thereby, the data amount for 160 frames are 160×64=10240bits. The number of frames required for transmitting these using thetransmission path frame is 10240/72=142.22 . . . , and therefore thetransmission data for 160 frames can be transmitted by using 143transmission path frames.

The transmission data frames each of which has been thus obtained bypacketizing all the transmission data as 64 bits (FIG. 22( c)) aresequentially combined (FIG. 22( b)), and thereafter are transmitted 72bits by 72 bits using transmission path frames (FIG. 22( a)). In FIG.22, the transmission data frames 1,2, . . . are transmitted in thetransmission path frames 5,6, . . . respectively in this order, and thetransmission of a total of 10240 bits of up to the transmission pathframe 147, that is, 160 transmission data frames are completed. Then,the significant data 2202 of 10240−72×142=16 bits are transmitted in thelast transmission path frame 147, and the remaining 56 bits areinsignificant data 2203 (refer to FIG. 22( a) and FIG. 22( b)). Byrepeating these, the transmission data frames are continuouslytransmitted to the side of the reception apparatus 1520.

Then, in this eighth embodiment, the data for packet synchronizationbetween the transmission apparatus 1510 and the reception apparatus 1520are accommodated in the transmission path frames 1 to 4 which have notbeen used for the transmission of the transmission data frames. Forexample, in the transmission apparatus 1510, all the data of thetransmission path frame 1 is set to “1”, and the reception apparatus1520 identifies the transmission path frame in which all the data is setto “1” as the transmission path frame 1 at the time of detecting thetransmission path frame, and recognizes that a data packet starts fromthe transmission path frame 5 which is the fifth frame counting from thetransmission path frame 1.

Then, the arbitrary data, for example, user data, or music data in thecase of transmitting audio data as significant data, may be accommodatedin the transmission path frames 2 to 4 and transmitted.

Hereinafter, the transmission process will be described with referenceto the drawings. FIG. 23 is a diagram illustrating a process flow chartof the transmission apparatus in this eighth embodiment. When the flowstarts (step 2300), the transmission data are input from the datageneration means 1511 to the transmission-side buffer means 114. Thetransmission-side buffer control means 115 monitors the accumulated dataamount in the transmission-side buffer means 114 and, when a certainvalue, for example, 2 frames of data are accumulated (step 2301),instructs the data packet generation means 1513 to start data output(step 2302). That is, the data packet generation means 1513 initiallytransmits the transmission path frames 1 to 4 in synchronization withthe timing of the transmission path clock (step 2303). Then, the datapacket generation means 1513 reads 1 frame of data from thetransmission-side buffer means (step 2304). Then, when the data packetgeneration means 1513 does not hold data for 1 transmission path frame,that is, data of 72 bits in this eighth embodiment, which are to besubsequently transmitted (step 2305), the process returns to step 2304,and 1 frame of transmission data are read from the transmission-sidebuffer means 114.

Then, when the timing of outputting data to the transmission path framecomes (step 2306), 1 transmission path frame of data, that is, 72 bitsof data in this eighth embodiment, are output to the transmission path(step 2307). Then, processes of step 2305 to step 2307 are repeateduntil the data packet generation means 1513 outputs the transmissionpath frame 146 in FIG. 22 (step 2308), and when the timing of outputtingdata to the transmission path frame comes (step 2310), the insignificantdata of 56 bits are added to the last 16 bits of data in thetransmission data frame 160 and the resultant is transmitted as thetransmission path frame 147 (step 2311). Then, the output of thetransmission path frame 147 is completed (step 2308), and then theprocesses of step 2303 to step 2311 are repeated. Thereby, packets arecontinuously transmitted.

FIG. 24 is a diagram illustrating a process flow chart of the receptionapparatus in this eighth embodiment. When the flow starts (step 2400),the reception apparatus 1520 receives the transmission path frame (step2401), and when the data of the transmission path frame includesynchronization data indicating transmission path frame 1 (step 2402),the process is started (step 2403). Subsequently, the data extractionmeans 1523 receives the transmission path frame 2 to transmission pathframe 4 subsequent to the transmission path frame 1 (step 2404), and thedata extraction means 1523 subsequently receives the transmission pathframe (step 2405). Then, the data extraction means 1523 reconstructs thetransmission data frame from the received transmission path frame, andoutputs the reconstructed frame to the reception-side buffer means 1524(step 2406). Then, processes of step 2405 to step 2406 are repeateduntil the transmission path frame 147 in FIG. 22 is received, and theprocess of the transmission path frame 147 is completed (step 2407), andthen processes of step 2401 to step 2408 are repeated. Then, theinsignificant bits 2203 which have been added by the transmissionapparatus 1510 are discarded from the transmission path frame 147 (referto FIG. 22( a)).

Then, data accumulated in the reception-side buffer 1524 are read withthe same clock as the transmission data clock in the transmissionapparatus 1510, and are transmitted to the data processing means 121.

In this way, according to this eighth embodiment, in a case where whilethe clock source of the data generation means 1511 and the clock sourceof the transmission path 100 are the same, the clock rate of thetransmission data output from the data generation means 1511 isdifferent from the clock rate of the transmission path 100, that is, ina system operating based on the transmission data clock of 48 kHz andthe transmission path clock of 44.1 kHz, the transmission apparatus 1510creates the transmission path clock from the transmission data clock inthe first clock control means 1501, and sequentially combines thetransmission data frames and thereafter transmits the frames 72 bits by72 bits with using the transmission path frame, and the receptionapparatus 1520 receives the transmission path frame and the transmissionpath clock and creates the transmission data clock from the transmissionpath clock in the second clock control means 1527, and outputs thetransmission data to the data processing means 121 on the basis of thetransmission data clock, and therefore the synchronized transmissionbetween the transmission apparatus 1510 and the reception apparatus 1520can be realized. Further, in this eighth embodiment, since thetransmission data is not omitted and all the data are transmitted, theprocesses in the data packet generation means 1513 on the side of thetransmission apparatus 1510, or the processes in the data extractionmeans on the side of the reception apparatus 1520 are reduced.

Then, while in this eighth embodiment the transmission data clock isoutput from the data generation means 1511 to the transmission apparatus1510 and the first clock control means generates the transmission pathclock, any configuration may be adopted as long as the configuration isone in which the transmission data clock and the transmission path clockare generated from the same clock source. For example, the configurationmay be one in which the first clock control means exists in anotherapparatus on the transmission path 100, and in this case, the datageneration means 1511 receives the transmission path clock generated bythe first clock control means 1501 in the other apparatus, and generatesthe transmission data clock from the received transmission path clock.

Further, while in this eighth embodiment each of 64 bits of thetransmission path frame 1 accommodates “1”, it is not necessarilyrestricted to this value. For example, a frame other than thetransmission path frame 1 may be for synchronization, or a plurality offrames may be used for synchronization. Further, only one or more bitsof the frame may be used as a mark for the synchronization data 2201,and the other bits may be used for another purpose, for example, forarbitrary data.

Further, while shown in this eighth embodiment is a system where thetransmission data frame is transmitted on the basis of 48 kHz and thetransmission path frame is transmitted on the basis of 44.1 kHz, theyare not restricted to these numeric values, and any system is applicableby changing the number of transmission data frames and the number oftransmission path frames as long as the system is one in which the clocksources of the transmission data frame and the transmission path frameare common. For example, in a system where the transmission data frameis transmitted on the basis of 48 kHz and the transmission path frame istransmitted on the basis of 44.1 kHz, the synchronization relationshipthat while 147 transmission data frames are input, 160 transmission pathframes are transmitted, is established, and therefore in a case wherewhen the data for 1 transmission path frame are of 64 bits, atransmission path for transmitting 64 bits in 1/48000 second isreserved, data can be transmitted using 147 transmission path frames andthe remaining 13 transmission path frames can be used for thetransmission of synchronization data 2201 and arbitrary data.

Embodiment 9

Next, a data transmission system and data transmission method accordingto this ninth embodiment will be described. This ninth embodiment ischaracterized in that a method at the transmission to the transmissionpath is different from that of the above-described eighth embodiment.Hereinafter, a description will be made with reference to the drawings.Then, an apparatus configuration in this ninth embodiment is similar tothat shown in FIG. 15, and the detailed description is omitted here.

FIG. 25 is a diagram illustrating a method of transmitting transmissiondata frames in this ninth embodiment. Then, in this ninth embodiment,the relationship between the clock of the transmission data and theclock of the transmission path frame is the same as that of theabove-described eighth embodiment. That is, 160 transmission data framesare transmitted with using 147 transmission path frames, therebyestablishing proper synchronization relationship.

In this ninth embodiment, as shown in FIG. 25( a), 1 bit of dummy data2502 is added to the heads of the transmission path frames other thanthe transmission path frames including synchronization data 2501. Thedummy data 2502 is for discriminating between the transmission pathframes and the transmission path frames including synchronization data2501 in the reception apparatus 1520.

Then, in this ninth embodiment, all the bits of the synchronization data2501 are set to “1” and the dummy data 2502 is set to “0”. By suchdefinition, there arises no cases where all the bits of the transmissionpath frames other than the transmission path frames including thesynchronization data 2501 are set to “1”, an erroneous detection of thetransmission path frames including the synchronization data 2501 iseliminated, thereby performing more reliable transmission.

To be specific, in this ninth embodiment, 64 bits of transmission dataframe obtained by omitting nothing, which is shown in FIG. 25( c), aretransmitted. Hence, the data amount for 160 frames are 160×64=10240bits. The number of frames required for transmitting these with usingthe transmission path frame is 10240/71=144.25 . . . since bits otherthan 1 bit of dummy data 2502 are used for transmission of thesignificant data 2503, and therefore 160 frames of transmission data canbe transmitted by using 145 transmission path frames.

The transmission data frames, each of which is thus obtained bypacketizing as 64 bits all the transmission data (FIG. 25( c)), aresequentially combined (FIG. 25( b)), and thereafter are transmitted 71bits by 71 bits with using the transmission path frame (FIG. 25( a)). InFIG. 25, the transmission data frames 1,2, . . . are transmitted in thetransmission path frames 3,4, . . . respectively in this order, and thetransmission of a total of 10240 bits of up to the transmission pathframe 147, that is, 160 transmission frames, is completed. Then, thesignificant data 2503 of 10240−71×144=16 bits are transmitted in thelast transmission path frame 147, and the remaining 55 bits areinsignificant data 2504 (refer to FIG. 25( a) and FIG. 25( b)). Byrepeating these, the transmission data frames are continuouslytransmitted to the side of the reception apparatus 1520.

Then, the arbitrary data, for example, user data, the music data in thecase of transmitting audio data as significant data, or the like, may beaccommodated in the transmission path frame 2 and transmitted.

In this way, according to this ninth embodiment, in a system operatingbased on the transmission data clock of 48 kHz and the transmission pathclock of 44.1 kHz, the transmission apparatus 1510 creates thetransmission path clock from the transmission data clock in the firstclock control means 1501, sequentially combines the transmission dataframes and thereafter transmits the frames 71 bits by 71 bits, which areadded to 1 bit of dummy data, by using the transmission path frame, andthe reception apparatus 1520 receives the transmission path frame andthe transmission path clock, and creates the transmission data clockfrom the transmission path clock in the second clock control means 1527,and outputs the transmission data to the data processing means 121 onthe basis of the transmission data clock, thereby realizing thesynchronized transmission between the transmission apparatus 1510 andthe reception apparatus 1520.

Then, also in this ninth embodiment, as in the above-described eighthembodiment, any configuration may be adopted as long as theconfiguration is one in which the transmission data clock and thetransmission path clock are generated from the same clock source.

Further, a method of packet reception synchronization in this ninthembodiment is an example, and the method is not necessarily restrictedthereto. For example, the transmission path frame 2 may be used for thetransmission of arbitrary data. Further, it is not necessary that thewhole transmission path frame 1 accommodate the synchronization data,and a portion of bits of the transmission path frame are used for thetransmission of the synchronization data, and the other bits may be usedfor another purpose, for example, for the transmission of arbitrary dataand the like.

Further, while in this ninth embodiment a system where the transmissiondata frame is transmitted on the basis of 48 kHz and the transmissionpath frame is transmitted on the basis of 44.1 kHz is shown, they arenot restricted to these numeric values, and any system is applicable bychanging the number of transmission data frames and the number oftransmission path frames as long as the system is one in which the clocksources of the transmission data frame and the transmission path frameare common.

Further, a method of preventing an erroneous detection of thetransmission path frame including the synchronization data which is usedin this ninth embodiment, is also applicable to the above-describedsixth embodiment or seventh embodiment. For example, when theabove-described method of preventing an erroneous detection is appliedto the above-described seventh embodiment, 63 bits among 64 bits whichare reserved in each of the transmission path frames for transmittingthe significant data 2001 in FIG. 21 are used for transmitting thesignificant data 2001, and 1 bit is used as dummy data. At this time,since 8640÷63=137.14 . . . , 138 transmission path frames, that is,transmission path frame 10 to transmission path frame 147, are used forthe transmission of the significant data 2001. Only 8640−63×137=9 bitsare transmitted in the last transmission path frame 147, and theremaining 54 bits (=63−9) are insignificant data. Also in this case, thetransmission path frame 1 is used as a frame including synchronizationdata 2002, and the transmission path frame 2 to transmission path frame9 may be used for the transmission of user data in a like manner. Then,in this case, the first 1 bit of each of the transmission path frame 2to transmission path frame 9 is the dummy data and the remaining 63 bitsare used for the transmission of the user data.

Further, while in the above-described first to ninth embodiments, caseswhere IEC60958 is used as a format of the transmission data and MOST isused as transmission path 100 are described, also when anothertransmission data format or another transmission path is used, they areapplicable in a like manner.

Further, the numeric values used in the above-described first to ninthembodiments are examples, and the numeric values are not restricted tothese values in actual operation.

Further, the packet formats shown in the above-described first toseventh embodiments are examples, and the location of each field on thepacket and the like can be arbitrarily changed.

Further, the number of transmission path frames including thesynchronization data shown in FIG. 17, FIG. 21, FIG. 22, and FIG. 25 inthe above-described sixth to ninth embodiments or the location of thedummy data on the transmission path frame shown in FIG. 25 in theabove-described ninth embodiment is an example, and they can bearbitrarily changed.

Further, while in the above-described first to ninth embodiments, theconfigurations in which the data generation means exist outside thetransmission apparatus are shown, the present invention can be similarlyrealized in a configuration in which the data generation means isincluded in the transmission apparatus.

Further, while in these first to ninth embodiments, the configurationsin which the data processing means exist outside the reception apparatusare shown, the present invention can be similarly realized in aconfiguration in which the data processing means is included in thereception apparatus.

Further, while in these first to seventh embodiments, the preamble andparity portions are omitted in the transmission apparatus, a format inwhich one of them, for example, a parity, is not omitted may betransmitted to the reception apparatus. Further, the configuration maybe one where when fields other than these, which are not used in thetransmission, are present, the transmission apparatus can omit thefields similarly to increase spare bits.

Further, while in these first to seventh embodiments, 1 frame oftransmission data is used as a processing unit, the present inventioncan be similarly realized also when a plurality of frames are used as aprocessing unit.

A data transmission system as well as data transmission method, datatransmission apparatus and data reception apparatus according to thepresent invention are useful as a system, method and apparatuses whichcan maintain synchronization between the transmission and reception evenwhen the transmission apparatus, the reception apparatus and thetransmission path do not operate on the same clock.

1. A data transmission system comprising a transmission apparatus and areception apparatus, the transmission apparatus and the receptionapparatus being connected via a transmission path, and data beingtransmitted from the transmission apparatus to the reception apparatusin an access unit that appears at a certain time interval and isallocated for the transmission path, wherein the transmission apparatuscomprises a data packet generation means for: receiving transmissiondata (i) composed of consecutive data frames and (ii) having, for atleast one data frame, a format that includes at least one of a preambleindicating a start of the data frame and a parity for detecting an errorin the data frame; omitting the at least one of the preamble and theparity from one or more data frames included in the transmission datareceived within the certain time interval; adding, to one or more dataframes (i) included in the received transmission data and (ii) havingthe at least one of the preamble and the parity omitted therefrom, adata length field indicating a number of bits of significant data;setting a remaining spare portion, of a data packet generated by thedata packet generation means, as spare bits; and adjusting a length ofthe spare bits according to a difference between a clock rate used bythe transmission apparatus and a clock rate used by the transmissionpath, to generate the data packet, including the one or more dataframes, the data length field and the adjusted spare bits, as the accessunit that is an entire length of the generated data packet, and whereinthe reception apparatus comprises a data extraction means for receivingthe access unit, and for adding, to the generated data packet of thereceived access unit, the at least one of the preamble and the parityomitted by the data packet generation means, to reconstruct the one ormore data frames included in the transmission data received by the datapacket generation means.
 2. The data transmission system as defined inclaim 1, wherein the reception apparatus comprises: a buffer means fortemporarily accumulating the one or more data frames reconstructed bythe data extraction means; and a buffer control means for monitoring anamount of accumulated data accumulated in the buffer means and adjustinga data reading rate of the buffer means according to an increase ordecrease in the amount of accumulated data.
 3. The data transmissionsystem as defined in claim 1, wherein the transmission apparatuscomprises a time-information generation means for generating, as timeinformation, a time that is based on a clock of the transmission data,wherein the data packet generation means adds, to the one or more dataframes included in the received transmission data and having the atleast one of the preamble and the parity omitted therefrom, thegenerated time information, and sets the remaining spare portion asspare bits, and wherein the reception apparatus comprises: a buffermeans for temporarily accumulating the one or more data framesreconstructed by the data extraction means; a clock control means forreproducing the time information generated by the time-informationgeneration means, the time information being obtained by the dataextraction means from the access unit received from the data packetgeneration means; and a buffer control means for adjusting a datareading rate of the buffer means based on a clock synchronized with thegenerated time represented by the time information reproduced by theclock control means.
 4. The data transmission system as defined in claim1, wherein, the data packet generation means (i) adds, to the one ormore data frames included in the received transmission data and havingthe at least one of the preamble and the parity omitted therefrom, apreamble location pointer indicating a location of a first preamble inthe one or more data frames, and a type of the first preamble, the firstpreamble being indicated by the preamble location pointer and the datalength field, and (ii) sets the remaining spare portion as spare bits.5. The data transmission system as defined in claim 1, wherein, thetransmission data format includes, for at least one data frame, aspecific field having a value specific to an application, wherein thedata packet generation means omits the specific field from the one ormore data frames, and wherein the data extraction means adds, to thegenerated data packet of the received access unit, the specific field,to reconstruct the one or more data frames included in the transmissiondata received by the data packet generation means.
 6. The datatransmission system as defined in claim 1, wherein the data length fieldindicates a number of bits of the spare bits.
 7. A data transmissionsystem comprising a transmission apparatus and a reception apparatus,the transmission apparatus and the reception apparatus being connectedvia a transmission path, and data being transmitted from thetransmission apparatus to the reception apparatus in an access unit thatappears at a certain time interval and is allocated for the transmissionpath, wherein the transmission apparatus comprises a data packetgeneration means for: receiving transmission data (i) composed ofconsecutive data frames and (ii) having a data transfer rate that isestablished from an integer ratio related to a data transfer rateallocated for the transmission path; making a plurality of data framesfrom the received transmission data, the plurality of data framesforming a processing unit, and the plurality of data frames having atime length that corresponds to an integer multiple of the time intervalat which the access unit appears; and dividing data comprised of thedata frames of the processing unit into an amount of data that can beaccommodated in the access unit, to form the data of the access unitfrom the divided data and wherein the reception apparatus comprises adata extraction means for receiving one or more access units,reconstructing the processing unit from the data of the one or morereceived access units, and reconstructing, from the data of thereconstructed processing unit, the consecutive data frames of thetransmission data.
 8. The data transmission system as defined in claim7, wherein the data packet generation means adds one or more bits ofsynchronization data indicating a start of the processing unit to one ormore access units, and wherein the data extraction means detects thestart of the processing unit by receiving the synchronization data. 9.The data transmission system as defined in claim 8, wherein the datapacket generation means adds, into a position in the access unit thatthe synchronization is not added, one or more bits of discriminationdata, the one or more bits of the discrimination data being differentfrom a value of the synchronization data, and the discrimination dataindicating that the synchronization data is not included in the accessunit.
 10. A data transmission system comprising a transmission apparatusand a reception apparatus, the transmission apparatus and the receptionapparatus being connected via a transmission path, and data beingtransmitted from the transmission apparatus to the reception apparatusin an access unit that appears at a certain time interval and isallocated for the transmission path, wherein the transmission apparatuscomprises a data packet generation means for: receiving transmissiondata (i) composed of consecutive data frames, (ii) having a datatransfer rate that is established from an integer ratio related to adata transfer rate allocated for the transmission path, and (iii)having, for at least one data frame, a format that includes at least oneof a preamble indicating a start of the data frame and a parity fordetecting an error in the data frame; omitting the at least one of thepreamble and the parity from each data frame of the plurality of dataframes that have a time length that corresponds to an integer multipleof the time interval at which the access unit appears; forming aprocessing unit from the data frames included in the receivedtransmission data and having the at least one of the preamble and theparity omitted therefrom; and dividing data comprised of the data framesof the processing unit into an amount of data that can be accommodatedin the access unit, to form the data of the access unit from the divideddata, and wherein the reception apparatus comprises a data extractionmeans for receiving one or more access units, for reconstructing theprocessing unit from the data of the one or more received access units,and for adding, to the reconstructed processing unit, the at least oneof the preamble and the parity omitted by the data packet generationmeans, to reconstruct the data frames included in the transmission datareceived by the data packet generation means.
 11. The data transmissionsystem as defined in claim 10, wherein the data packet generation meansadds one or more bits of synchronization data indicating a start of theprocessing unit to one or more access units, and wherein the dataextraction means detects the start of the processing unit by receivingthe synchronization data.
 12. The data transmission system as defined inclaim 11, wherein the data packet generation means adds, into a positionin the access unit that the synchronization is not added, one or morebits of discrimination data, the one or more bits of the discriminationdata being different from a value of the synchronization data, and thediscrimination data indicating that the synchronization data is notincluded in the access unit.
 13. The data transmission system as definedin claim 10, wherein the transmission data format includes a specificfield having a value specific to an application, wherein the data packetgeneration means omits the specific field from each data frame of theplurality of data frames that have the time length that corresponds tothe integer multiple of the time interval at which the access unitappears, and wherein the data extraction means adds, to thereconstructed processing unit, the specific field, to reconstruct thedata frames included in the transmission data received by the datapacket generation means.
 14. The data transmission system as defined inclaim 1, wherein the transmission data format is a format defined byIEC60958-1 First Edition 1999-12.
 15. The data transmission system asdefined in claim 1, wherein the transmission path is a serial bus.
 16. Adata transmission apparatus connected to a transmission path thattransmits data in an access unit allocated for the transmission path,the data transmission apparatus comprising a data packet generationmeans for: receiving transmission data (i) composed of consecutive dataframes and (ii) having, for at least one data frame, a format thatincludes at least one of a preamble indicating a start of the data frameand a parity for detecting an error in the data frame; omitting the atleast one of the preamble and the parity from one or more data framesincluded in the transmission data transmitted in the access unit;adding, to one or more data frames (i) included in the receivedtransmission data and (ii) having the at least one of the preamble andthe parity omitted therefrom, a data length field indicating a number ofbits of significant data; setting a remaining spare portion, of a datapacket generated by the data packet generation means, as spare bits; andadjusting a length of the spare bits according to a difference between aclock rate used by the transmission apparatus and a clock rate used bythe transmission path, to generate the data packet, including the one ormore data frames, the data length field and the adjusted spare bits, asthe access unit that is an entire length of the generated data packet.17. The data transmission apparatus as defined in claim 16, wherein thedata transmission apparatus comprises a time-information generationmeans for generating, as time information, a time that is based on aclock of the transmission data, and wherein the data packet generationmeans adds, to the one or more data frames included in the receivedtransmission data and having the at least one of the preamble and theparity omitted therefrom, the generated time information, and sets theremaining spare portion as spare bits.
 18. The data transmissionapparatus as defined in claim 16, wherein the data packet generationmeans (i) adds, to the one or more data frames included in the receivedtransmission data and having the at least one of the preamble and theparity omitted therefrom, a preamble location pointer indicating alocation of a first preamble in the one or more data frames, and a typeof the first preamble, the first preamble being indicated by thepreamble location pointer and the data length field, and (ii) sets theremaining spare portion as spare bits.
 19. The data transmissionapparatus as defined in claim 16, wherein the transmission data formatincludes, for at least one data frame, a specific field having a valuespecific to an application, and wherein the data packet generation meansomits the specific field from the one or more data frames.
 20. The datatransmission apparatus as defined in claim 16, wherein the data lengthfield indicates a number of bits of the spare bits.
 21. A datatransmission apparatus connected to a transmission path to which areception apparatus is connected, the data transmission apparatustransmitting data in an access unit that appears at a certain timeintervals and is allocated for the transmission path, the data beingtransmitted to the reception apparatus, the data transmission apparatuscomprising a data packet generation means for: receiving transmissiondata (i) composed of consecutive data frames and (ii) having a datatransfer rate that is established from an integer ratio related to adata transfer rate allocated for the transmission path, making aplurality of data frames from the received transmission data, theplurality of data frames forming a processing unit, and the plurality ofdata frames having a time length that corresponds to an integer multipleof the time interval at which the access unit appears; and dividing datacomprised of the data frames of the processing unit into an amount ofdata that can be accommodated in the access unit to form the data of theaccess unit from the divided data.
 22. The data transmission apparatusas defined in claim 21, wherein the data packet generation means addsone or more bits of synchronization data indicating a start of theprocessing unit to one or more access units.
 23. The data transmissionapparatus as defined in claim 22, wherein the data packet generationmeans adds, into a position in the access unit that the synchronizationis not added, one or more bits of discrimination data, the one or morebits of discrimination data being different from a value of thesynchronization data, and the discrimination data indicating that thesynchronization data is not included in the access unit.
 24. A datatransmission apparatus connected to a transmission path that transmitsdata in an access unit that appears at a certain time interval and isallocated for the transmission path, the data transmission apparatuscomprising a data packet generation means for: receiving transmissiondata (i) composed of consecutive data frames, (ii) having a datatransfer rate that is established from an integer ratio related to adata transfer rate allocated for the transmission path, and (iii)having, for at least one data frame, a format that includes at least oneof a preamble indicating a start of the data frame and a parity fordetecting an error in the data frame; omitting the at least one of thepreamble and the parity from each data frame of the plurality of dataframes that have a time length that corresponds to an integer multipleof the time interval at which the access unit appears; forming aprocessing unit from the data frames included in the receivedtransmission data and having the at least one of the preamble and theparity omitted therefrom; and dividing data comprised of the data framesof the processing unit into an amount of data that can be accommodatedin the access unit, to form the data of the access unit from the divideddata.
 25. The data transmission apparatus as defined in claim 24,wherein the data packet generation means adds one or more bits ofsynchronization data indicating a start of the processing unit to one ormore access units.
 26. The data transmission apparatus as defined inclaim 25, wherein the data packet generation means adds, into a positionin the access unit that the synchronization is not added, one or morebits of discrimination data, the one or more bits of the discriminationdata being different from a value of the synchronization data, and thediscrimination data indicating that the synchronization data is notincluded in the access unit.
 27. The data transmission apparatus asdefined in claim 24, wherein the transmission data format includes aspecific field having a value specific to an application, and whereinthe data packet generation means omits the specific field from each dataframe of the plurality of data frames that have the time length thatcorresponds to the integer multiple of the time interval at which theaccess unit appears.
 28. The data transmission apparatus as defined inclaim 16, wherein the transmission data format is a format defined byIEC60958-1 First Edition 1999-12.
 29. The data transmission apparatus asdefined in claim 16, wherein the transmission path is a serial bus. 30.A data reception apparatus that is connected to a transmission path andthat receives, from a transmission apparatus, a data packet generated by(i) omitting at least one of a preamble indicating a start of a dataframe and a parity for detecting an error in the data frame, from one ormore data frames included in transmission data and transmitted in anaccess unit that appears at a certain time interval and is allocated forthe transmission path, (ii) adding, to one or more data frames includedin the transmission data and having the at least one of the preamble andthe parity omitted therefrom, a data length field indicating a number ofbits of significant data, (iii) setting a remaining spare portion of thedata packet as spare bits, and (iv) adjusting a length of the spare bitsaccording to a difference between a clock rate used by the transmissionapparatus and a clock rate used by the transmission path, to generatethe data packet, including the one or more data frames, the data lengthfield and the adjusted spare bits, as the access unit that is an entirelength of the generated data packet, the data reception apparatuscomprising a data extraction means for receiving the access unit and foradding, to the generated data packet of the received access unit, the atleast one of the preamble and the parity omitted from the one or moredata frames, to reconstruct the one or more data frames included in thetransmission data.
 31. The data reception apparatus as defined in claim30, comprising: a buffer means for temporarily accumulating the one ormore data frames reconstructed by the data extraction means; and abuffer control means for monitoring an amount of accumulated dataaccumulated in the buffer means and adjusting a data reading rate of thebuffer means according to an increase or decrease in the amount ofaccumulated data.
 32. The data reception apparatus as defined in claim30, comprising: a buffer means for temporarily accumulating the one ormore data frames reconstructed by the data extraction means; a clockcontrol means for reproducing a time from time information obtained bythe data extraction means from the received access unit; and a buffercontrol means for adjusting a data reading rate of the buffer meansbased on a clock synchronized with the time reproduced by the clockcontrol means.
 33. A data reception apparatus that is connected to atransmission path and that receives, from a transmission apparatus, datatransmitted in an access unit that appears at a certain time intervaland is allocated for the transmission path, the data reception apparatuscomprising a data extraction means for: receiving the access unitobtained by (i) omitting at least one of a preamble indicating a startof a data frame and a parity for detecting errors in the data frame,from each data frame of a plurality of data frames included intransmission data received by the transmission apparatus that have atime length that corresponds to an integer multiple of the time intervalat which the access unit appears, (ii) forming a processing unit fromthe data frames included in the transmission data and having the atleast one of the preamble and the parity omitted therefrom, and (iii)dividing data comprised of the data frames of the processing unit intoan amount of data that can be accommodated in the access unit;reconstructing the processing unit from the data of the received accessunit; and adding, to the reconstructed processing unit, the at least oneof the preamble and the parity omitted from each data frame, toreconstruct the data frames included in the transmission data.
 34. Thedata reception apparatus as defined in claim 33, wherein the dataextraction means detects a start of the processing unit by receiving oneor more access units including one or more bits of synchronization dataindicating the start of the processing unit.
 35. The data receptionapparatus as defined in claim 30, wherein the transmission data formatincludes a specific field having a value specific to an application, andwherein the data extraction means adds the specific field to the data ofthe received access unit.
 36. The data reception apparatus as defined inclaim 30, wherein the transmission data format is a format defined byIEC60958-1 First Edition 1999-12.
 37. The data reception apparatus asdefined in claim 30, wherein the transmission path is a serial bus. 38.A data transmission method comprising: a data packet generation step of:omitting at least one of a preamble indicating a start of a data frameand a parity for detecting an error in the data frame from one or moredata frames included in transmission data (i) composed of consecutivedata frames and (ii) having, for at least one data frame, a format thatincludes the at least one of the preamble and the parity; adding, to oneor more data frames (i) included in the received transmission data and(ii) having the at least one of the preamble and the parity omittedtherefrom, a data length field indicating a number of bits ofsignificant data; setting a remaining spare portion, of the data packetto be generated, as spare bits; adjusting a length of the spare bitsaccording to a difference between a clock rate used by a transmissionapparatus that transmits the generated data packet on a transmissionpath and a clock rate used by the transmission path; generating the datapacket including the one or more data frames, the data length field andthe adjusted spare bits, the data packet being generated as an accessunit, and the access unit being allocated for the transmission path overan entire length of the generated data packet; and a data extractionstep of receiving the access unit and adding, to the generated datapacket of the received access unit, the at least one of the preamble andthe parity omitted in the data packet generation step, to reconstructthe one or more data frames included in the transmission data.
 39. Thedata transmission method as defined in claim 38, wherein thetransmission data format includes, for at least one data frame, aspecific field having a value specific to an application, wherein thedata packet generation step omits the specific field from the one ormore data frames, and wherein the data extraction step adds, to thegenerated data packet of the received access unit, the specific field,to reconstruct the one or more data frames included in the transmissiondata.
 40. A data transmission method of using a transmission system,which includes a transmission apparatus and a reception apparatus, fortransmitting data in an access unit that appears at a certain timeinterval, the access unit being allocated to a transmission path, thedata transmission method comprising: a data packet generation step of:receiving transmission data (i) composed of consecutive data frames and(ii) having a data transfer rate that is established from an integerratio related to a data transfer rate allocated for the transmissionpath; making a plurality of data frames from the received transmissiondata, the plurality of data frames forming a processing unit, and theplurality of data frames having a time length that corresponds to aninteger multiple of the time interval at which the access unit appearsand; and dividing data comprised of the data frames of the processingunit into an amount of data that can be accommodated in the access unit,to form the data of the access unit from the divided data; and a dataextraction step of receiving the one or more access units,reconstructing the processing unit from the data of the one or morereceived access units, and reconstructing, from the data of thereconstructed processing unit, the consecutive data frames of thetransmission data.
 41. A data transmission method of using atransmission system, which includes a transmission apparatus and areception apparatus, for transmitting data in an access unit thatappears at a certain time interval, the access unit being allocated to atransmission path, and the data transmission method comprising: a datapacket generation step of: receiving transmission data (i) composed ofconsecutive data frames, (ii) having a data transfer rate that isestablished from an integer ratio related to a data transfer rateallocated for the transmission path, and (iii) having, for at least onedata frame, a format that includes at least one of a preamble indicatinga start of the data frame and a parity for detecting an error in thedata frame; omitting the at least one of the preamble and the parityfrom each data frame of the plurality of data frames that have a timelength that corresponds to an integer multiple of the time interval atwhich the access unit appears; forming a processing unit from the dataframes included in the received transmission data and having the atleast one of the preamble and the parity omitted therefrom; and dividingdata comprised of the data frames of the processing unit into an amountof data that can be accommodated in the access unit to form the data ofthe access unit from the divided data; and a data extraction step ofreceiving one or more access units, reconstructing the processing unitfrom the data of the one or more received access units, adding, to thereconstructed processing unit, the at least one of the preamble and theparity omitted in the data packet generation step, to reconstruct thedata frames included in the transmission data.
 42. The data transmissionmethod as defined in claim 41, wherein the transmission data formatincludes a specific field having a value specific to an application,wherein the data packet generation step omits the specific field fromeach data frame of the plurality of data frames that have the timelength that corresponds to the integer multiple of the time interval atwhich the access unit appears, and wherein the data extraction stepadds, to the reconstructed processing unit, the specific field, toreconstruct the data frames included in the transmission data receivedby the data packet generation means.
 43. The data transmission system asdefined in claim 10, wherein the transmission data format is a formatdefined by IEC60958-1 First Edition 1999-12.
 44. The data transmissionsystem as defined in claim 7, wherein the transmission path is a serialbus.
 45. The data transmission system as defined in claim 10, whereinthe transmission path is a serial bus.
 46. The data transmissionapparatus as defined in claim 24, wherein the transmission data formatis a format defined by IEC60958-1 First Edition 1999-12.
 47. The datatransmission apparatus as defined in claim 21, wherein the transmissionpath is a serial bus.
 48. The data transmission apparatus as defined inclaim 24, wherein the transmission path is a serial bus.
 49. The datareception apparatus as defined in claim 33, wherein the transmissiondata format includes a specific field having a value specific to anapplication, and wherein the data extraction means adds the specificfield to the reconstructed processing unit.
 50. The data receptionapparatus as defined in claim 33, wherein the transmission data formatis a format defined by IEC60958-1 First Edition 1999-12.
 51. The datareception apparatus as defined in claim 33, wherein the transmissionpath is a serial bus.